merge: dev

this is another one of those standards-defining things like
`vc-requiredPlugins`, but i do genuinely think passing the client mod
that's in use here will be beneficial in the long run for usercss
authors since they can write one file that works across multiple.
hopefully other mods that implement usercss will adopt this 🤞

browser/VencordNativeStub.ts

@@ -25,7 +25,6 @@ import * as DataStore from "../src/api/DataStore";
 import { debounce } from "../src/utils";
 import { EXTENSION_BASE_URL } from "../src/utils/web-metadata";
 import { getTheme, Theme } from "../src/utils/discord";
-import { getThemeInfo } from "../src/main/themes";
 
 // Discord deletes this so need to store in variable
 const { localStorage } = window;
@@ -46,7 +45,7 @@ window.VencordNative = {
         deleteTheme: (fileName: string) => DataStore.del(fileName, themeStore),
         getThemesDir: async () => "",
         getThemesList: () => DataStore.entries(themeStore).then(entries =>
-            entries.map(([name, css]) => getThemeInfo(css, name.toString()))
+            entries.map(([name, css]) => ({ fileName: name as string, content: css }))
         ),
         getThemeData: (fileName: string) => DataStore.get(fileName, themeStore),
         getSystemValues: async () => ({}),

package.json

@@ -39,15 +39,19 @@
         "gifenc": "github:mattdesl/gifenc#64842fca317b112a8590f8fef2bf3825da8f6fe3",
         "monaco-editor": "^0.43.0",
         "nanoid": "^4.0.2",
+        "usercss-meta": "^0.12.0",
         "virtual-merge": "^1.0.1"
     },
     "devDependencies": {
         "@types/chrome": "^0.0.246",
         "@types/diff": "^5.0.3",
+        "@types/less": "^3.0.4",
         "@types/lodash": "^4.14.194",
         "@types/node": "^18.16.3",
         "@types/react": "^18.2.0",
         "@types/react-dom": "^18.2.1",
+        "@types/stylus": "^0.48.39",
+        "@types/tinycolor2": "^1.4.3",
         "@types/yazl": "^2.4.2",
         "@typescript-eslint/eslint-plugin": "^5.59.1",
         "@typescript-eslint/parser": "^5.59.1",
@@ -75,7 +79,8 @@
     "pnpm": {
         "patchedDependencies": {
             "eslint-plugin-path-alias@1.0.0": "patches/eslint-plugin-path-alias@1.0.0.patch",
-            "eslint@8.46.0": "patches/eslint@8.46.0.patch"
+            "eslint@8.46.0": "patches/eslint@8.46.0.patch",
+            "@types/less@3.0.4": "patches/@types__less@3.0.4.patch"
         },
         "peerDependencyRules": {
             "ignoreMissing": [

patches/@types__less@3.0.4.patch

@@ -0,0 +1,13 @@
+diff --git a/index.d.ts b/index.d.ts
+index eb4f07d47b932fb9cc8c8cd451ab107f648bd013..18a3e15a1997734e1773718e5be55d252ed9478c 100644
+--- a/index.d.ts
++++ b/index.d.ts
+@@ -306,7 +306,5 @@ interface LessStatic {
+ }
+ 
+ declare module "less" {
+-    export = less;
++    export = LessStatic;
+ }
+-
+-declare var less: LessStatic;

pnpm-lock.yaml

@@ -1,6 +1,9 @@
 lockfileVersion: '6.0'
 
 patchedDependencies:
+  '@types/less@3.0.4':
+    hash: krcufrsfhsuxuoj7hocqugs6zi
+    path: patches/@types__less@3.0.4.patch
   eslint-plugin-path-alias@1.0.0:
     hash: m6sma4g6bh67km3q6igf6uxaja
     path: patches/eslint-plugin-path-alias@1.0.0.patch
@@ -33,6 +36,9 @@ dependencies:
   nanoid:
     specifier: ^4.0.2
     version: 4.0.2
+  usercss-meta:
+    specifier: ^0.12.0
+    version: 0.12.0
   virtual-merge:
     specifier: ^1.0.1
     version: 1.0.1
@@ -44,6 +50,9 @@ devDependencies:
   '@types/diff':
     specifier: ^5.0.3
     version: 5.0.3
+  '@types/less':
+    specifier: ^3.0.4
+    version: 3.0.4(patch_hash=krcufrsfhsuxuoj7hocqugs6zi)
   '@types/lodash':
     specifier: ^4.14.194
     version: 4.14.194
@@ -56,6 +65,12 @@ devDependencies:
   '@types/react-dom':
     specifier: ^18.2.1
     version: 18.2.1
+  '@types/stylus':
+    specifier: ^0.48.39
+    version: 0.48.39
+  '@types/tinycolor2':
+    specifier: ^1.4.3
+    version: 1.4.3
   '@types/yazl':
     specifier: ^2.4.2
     version: 2.4.2
@@ -564,6 +579,11 @@ packages:
     resolution: {integrity: sha512-wOuvG1SN4Us4rez+tylwwwCV1psiNVOkJeM3AUWUNWg/jDQY2+HE/444y5gc+jBmRqASOm2Oeh5c1axHobwRKQ==}
     dev: true
 
+  /@types/less@3.0.4(patch_hash=krcufrsfhsuxuoj7hocqugs6zi):
+    resolution: {integrity: sha512-djlMpTdDF+tLaqVpK/0DWGNIr7BFjN8ykDLkgS0sQGYYLop51imRRE3foTjl+dMAH1zFE8bMZAG0VbYPEcSgsA==}
+    dev: true
+    patched: true
+
   /@types/lodash@4.14.194:
     resolution: {integrity: sha512-r22s9tAS7imvBt2lyHC9B8AGwWnXaYb1tY09oyLkXDs4vArpYJzw09nj8MLx5VfciBPGIb+ZwG0ssYnEPJxn/g==}
     dev: true
@@ -613,6 +633,16 @@ packages:
     resolution: {integrity: sha512-21cFJr9z3g5dW8B0CVI9g2O9beqaThGQ6ZFBqHfwhzLDKUxaqTIy3vnfah/UPkfOiF2pLq+tGz+W8RyCskuslw==}
     dev: true
 
+  /@types/stylus@0.48.39:
+    resolution: {integrity: sha512-98a0QrJorrq8+Vsan9yfxol2Qr6nvUWBeV3oYnSMks4QdLMebAzZvRd9IuoZOcnB6Erfjcjn1J2J+63MPCxJnw==}
+    dependencies:
+      '@types/node': 18.16.3
+    dev: true
+
+  /@types/tinycolor2@1.4.3:
+    resolution: {integrity: sha512-Kf1w9NE5HEgGxCRyIcRXR/ZYtDv0V8FVPtYHwLxl0O+maGX0erE77pQlD0gpP+/KByMZ87mOA79SjifhSB3PjQ==}
+    dev: true
+
   /@types/yauzl@2.10.0:
     resolution: {integrity: sha512-Cn6WYCm0tXv8p6k+A8PvbDG763EDpBoTzHdA+Q/MF6H3sapGjCm9NzoaJncJS9tUKSuCoDs9XHxYYsQDgxR6kw==}
     requiresBuild: true
@@ -3309,6 +3339,11 @@ packages:
     engines: {node: '>=0.10.0'}
     dev: true
 
+  /usercss-meta@0.12.0:
+    resolution: {integrity: sha512-zKrXCKdpeIwtVe87omxGo9URf+7mbozduMZEg79dmT4KB3XJwfIkEi/Uk0PcTwR/nZLtAK1+k7isgbGB/g6E7Q==}
+    engines: {node: '>=8.3'}
+    dev: false
+
   /util-deprecate@1.0.2:
     resolution: {integrity: sha512-EPD5q1uXyFxJpCrLnCc1nHnq3gOa6DZBocAIiI2TaSCA7VCJ1UJDMagCzIkXNsUYfD1daK//LTEQ8xiIbrHtcw==}
     dev: true

src/VencordNative.ts

@@ -8,7 +8,6 @@ import { IpcEvents } from "@utils/IpcEvents";
 import { IpcRes } from "@utils/types";
 import { ipcRenderer } from "electron";
 import { PluginIpcMappings } from "main/ipcPlugins";
-import type { UserThemeHeader } from "main/themes";
 
 function invoke<T = any>(event: IpcEvents, ...args: any[]) {
     return ipcRenderer.invoke(event, ...args) as Promise<T>;
@@ -33,7 +32,7 @@ export default {
         uploadTheme: (fileName: string, fileData: string) => invoke<void>(IpcEvents.UPLOAD_THEME, fileName, fileData),
         deleteTheme: (fileName: string) => invoke<void>(IpcEvents.DELETE_THEME, fileName),
         getThemesDir: () => invoke<string>(IpcEvents.GET_THEMES_DIR),
-        getThemesList: () => invoke<Array<UserThemeHeader>>(IpcEvents.GET_THEMES_LIST),
+        getThemesList: () => invoke<Array<{ fileName: string; content: string; }>>(IpcEvents.GET_THEMES_LIST),
         getThemeData: (fileName: string) => invoke<string | undefined>(IpcEvents.GET_THEME_DATA, fileName),
         getSystemValues: () => invoke<Record<string, string>>(IpcEvents.GET_THEME_SYSTEM_VALUES),
     },

src/api/Settings.ts

@@ -75,6 +75,12 @@ export interface Settings {
         settingsSync: boolean;
         settingsSyncVersion: number;
     };
+
+    userCssVars: {
+        [themeId: string]: {
+            [varName: string]: string;
+        };
+    };
 }
 
 const DefaultSettings: Settings = {
@@ -107,7 +113,9 @@ const DefaultSettings: Settings = {
         url: "https://api.vencord.dev/",
         settingsSync: false,
         settingsSyncVersion: 0
-    }
+    },
+
+    userCssVars: {}
 };
 
 try {
@@ -125,7 +133,7 @@ const saveSettingsOnFrequentAction = debounce(async () => {
     }
 }, 60_000);
 
-type SubscriptionCallback = ((newValue: any, path: string) => void) & { _paths?: Array<string>; };
+type SubscriptionCallback = ((newValue: any, path: string) => void) & { _paths?: Array<string>; _exact?: boolean; };
 const subscriptions = new Set<SubscriptionCallback>();
 
 const proxyCache = {} as Record<string, any>;
@@ -182,7 +190,12 @@ function makeProxy(settings: any, root = settings, path = ""): Settings {
             const setPath = `${path}${path && "."}${p}`;
             delete proxyCache[setPath];
             for (const subscription of subscriptions) {
-                if (!subscription._paths || subscription._paths.includes(setPath)) {
+                if (
+                    !subscription._paths ||
+                    (subscription._exact
+                        ? subscription._paths.includes(setPath)
+                        : subscription._paths.some(p => setPath.startsWith(p)))
+                ) {
                     subscription(v, setPath);
                 }
             }
@@ -220,11 +233,14 @@ export const Settings = makeProxy(settings);
  * @returns Settings
  */
 // TODO: Representing paths as essentially "string[].join('.')" wont allow dots in paths, change to "paths?: string[][]" later
-export function useSettings(paths?: UseSettings<Settings>[]) {
+export function useSettings(paths?: UseSettings<Settings>[], exact = true) {
     const [, forceUpdate] = React.useReducer(() => ({}), {});
 
     const onUpdate: SubscriptionCallback = paths
-        ? (value, path) => paths.includes(path as UseSettings<Settings>) && forceUpdate()
+        ? (value, path) =>
+            (exact
+                ? paths.includes(path as UseSettings<Settings>)
+                : paths.some(p => path.startsWith(p))) && forceUpdate()
         : forceUpdate;
 
     React.useEffect(() => {
@@ -250,11 +266,12 @@ type ResolvePropDeep<T, P> = P extends "" ? T :
  * @example addSettingsListener("", (newValue, path) => console.log(`${path} is now ${newValue}`))
  *          addSettingsListener("plugins.Unindent.enabled", v => console.log("Unindent is now", v ? "enabled" : "disabled"))
  */
-export function addSettingsListener<Path extends keyof Settings>(path: Path, onUpdate: (newValue: Settings[Path], path: Path) => void): void;
-export function addSettingsListener<Path extends string>(path: Path, onUpdate: (newValue: Path extends "" ? any : ResolvePropDeep<Settings, Path>, path: Path extends "" ? string : Path) => void): void;
-export function addSettingsListener(path: string, onUpdate: (newValue: any, path: string) => void) {
+export function addSettingsListener<Path extends keyof Settings>(path: Path, onUpdate: (newValue: Settings[Path], path: Path) => void, exact?: boolean): void;
+export function addSettingsListener<Path extends string>(path: Path, onUpdate: (newValue: Path extends "" ? any : ResolvePropDeep<Settings, Path>, path: Path extends "" ? string : Path) => void, exact?: boolean): void;
+export function addSettingsListener(path: string, onUpdate: (newValue: any, path: string) => void, exact = true) {
     if (path)
         ((onUpdate as SubscriptionCallback)._paths ??= []).push(path);
+    (onUpdate as SubscriptionCallback)._exact = exact;
     subscriptions.add(onUpdate);
 }
 

src/components/Icons.tsx

@@ -256,6 +256,24 @@ export function DeleteIcon(props: IconProps) {
     );
 }
 
+/**
+ * A plugin icon, created by CorellanStoma. https://github.com/CreArts-Community/Settings-Icons
+ */
+export function PluginIcon(props: IconProps) {
+    return (
+        <Icon
+            {...props}
+            className={classes(props.className, "vc-plugin-icon")}
+            viewBox="0 0 24 24"
+        >
+            <path
+                fill="currentColor"
+                d="M20.5 11H19V7c0-1.1-.9-2-2-2h-4V3.5C13 2.12 11.88 1 10.5 1S8 2.12 8 3.5V5H4c-1.1 0-1.99.9-1.99 2v3.8H3.5c1.49 0 2.7 1.21 2.7 2.7s-1.21 2.7-2.7 2.7H2V20c0 1.1.9 2 2 2h3.8v-1.5c0-1.49 1.21-2.7 2.7-2.7s2.7 1.21 2.7 2.7V22H17c1.1 0 2-.9 2-2v-4h1.5c1.38 0 2.5-1.12 2.5-2.5S21.88 11 20.5 11z"
+            />
+        </Icon>
+    );
+}
+
 export function PlusIcon(props: IconProps) {
     return (
         <Icon
@@ -290,3 +308,40 @@ export function NoEntrySignIcon(props: IconProps) {
         </Icon>
     );
 }
+
+export function PasteIcon(props: IconProps) {
+    return (
+        <Icon
+            {...props}
+            className={classes(props.className, "vc-paste-icon")}
+            viewBox="0 0 24 24"
+            fill="none"
+            stroke="currentColor"
+            stroke-width="2"
+            stroke-linecap="round"
+            stroke-linejoin="round"
+        >
+            <rect width="8" height="4" x="8" y="2" rx="1" ry="1" />
+            <path d="M16 4h2a2 2 0 0 1 2 2v14a2 2 0 0 1-2 2H6a2 2 0 0 1-2-2V6a2 2 0 0 1 2-2h2" />
+        </Icon>
+    );
+}
+
+export function ResetIcon(props: IconProps) {
+    return (
+        <Icon
+            {...props}
+            width="24"
+            height="24"
+            viewBox="0 0 24 24"
+            fill="none"
+            stroke="currentColor"
+            stroke-width="2"
+            stroke-linecap="round"
+            stroke-linejoin="round"
+        >
+            <path d="M3 12a9 9 0 1 0 9-9 9.75 9.75 0 0 0-6.74 2.74L3 8" />
+            <path d="M3 3v5h5" />
+        </Icon>
+    );
+}

src/components/ThemeSettings/ThemesTab.tsx

@@ -16,25 +16,32 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
-import { useSettings } from "@api/Settings";
+import "./themesStyles.css";
+
+import { Settings, useSettings } from "@api/Settings";
 import { classNameFactory } from "@api/Styles";
 import { Flex } from "@components/Flex";
-import { DeleteIcon } from "@components/Icons";
+import { CogWheel, DeleteIcon, PluginIcon } from "@components/Icons";
 import { Link } from "@components/Link";
 import PluginModal from "@components/PluginSettings/PluginModal";
+import { AddonCard } from "@components/VencordSettings/AddonCard";
+import { SettingsTab, wrapTab } from "@components/VencordSettings/shared";
 import { openInviteModal } from "@utils/discord";
 import { Margins } from "@utils/margins";
 import { classes } from "@utils/misc";
 import { openModal } from "@utils/modal";
 import { showItemInFolder } from "@utils/native";
 import { useAwaiter } from "@utils/react";
+import type { ThemeHeader } from "@utils/themes";
+import { getThemeInfo, stripBOM, type UserThemeHeader } from "@utils/themes/bd";
+import { usercssParse } from "@utils/themes/usercss";
 import { findByPropsLazy, findLazy } from "@webpack";
-import { Button, Card, Forms, React, showToast, TabBar, TextArea, useEffect, useRef, useState } from "@webpack/common";
-import { UserThemeHeader } from "main/themes";
+import { Button, Card, Forms, React, showToast, TabBar, TextArea, Tooltip, useEffect, useMemo, useRef, useState } from "@webpack/common";
 import type { ComponentType, Ref, SyntheticEvent } from "react";
+import type { UserstyleHeader } from "usercss-meta";
 
-import { AddonCard } from "./AddonCard";
-import { SettingsTab, wrapTab } from "./shared";
+import { isPluginEnabled } from "../../plugins";
+import { UserCSSSettingsModal } from "./UserCSSModal";
 
 type FileInput = ComponentType<{
     ref: Ref<HTMLInputElement>;
@@ -49,6 +56,7 @@ const TextAreaProps = findLazy(m => typeof m.textarea === "string");
 
 const cl = classNameFactory("vc-settings-theme-");
 
+
 function Validator({ link }: { link: string; }) {
     const [res, err, pending] = useAwaiter(() => fetch(link).then(res => {
         if (res.status > 300) throw `${res.status} ${res.statusText}`;
@@ -97,14 +105,75 @@ function Validators({ themeLinks }: { themeLinks: string[]; }) {
     );
 }
 
-interface ThemeCardProps {
+interface OtherThemeCardProps {
     theme: UserThemeHeader;
     enabled: boolean;
     onChange: (enabled: boolean) => void;
     onDelete: () => void;
 }
 
-function ThemeCard({ theme, enabled, onChange, onDelete }: ThemeCardProps) {
+interface UserCSSCardProps {
+    theme: UserstyleHeader;
+    enabled: boolean;
+    onChange: (enabled: boolean) => void;
+    onDelete: () => void;
+    onSettingsReset: () => void;
+}
+
+function UserCSSThemeCard({ theme, enabled, onChange, onDelete, onSettingsReset }: UserCSSCardProps) {
+    const missingPlugins = useMemo(() =>
+        theme.requiredPlugins?.filter(p => !isPluginEnabled(p)), [theme]);
+
+    return (
+        <AddonCard
+            name={theme.name ?? "Unknown"}
+            description={theme.description}
+            author={theme.author ?? "Unknown"}
+            enabled={enabled}
+            setEnabled={onChange}
+            disabled={missingPlugins && missingPlugins.length > 0}
+            infoButton={
+                <>
+                    {missingPlugins && missingPlugins.length > 0 && (
+                        <Tooltip text={"The following plugins are required, but aren't enabled: " + missingPlugins.join(", ")}>
+                            {({ onMouseLeave, onMouseEnter }) => (
+                                <div
+                                    style={{ color: "var(--status-danger" }}
+                                    onMouseEnter={onMouseEnter}
+                                    onMouseLeave={onMouseLeave}
+                                >
+                                    <PluginIcon />
+                                </div>
+                            )}
+                        </Tooltip>
+                    )}
+                    {theme.vars && (
+                        <div style={{ cursor: "pointer" }} onClick={
+                            () => openModal(modalProps =>
+                                <UserCSSSettingsModal modalProps={modalProps} theme={theme} onSettingsReset={onSettingsReset} />)
+                        }>
+                            <CogWheel />
+                        </div>
+                    )}
+                    {IS_WEB && (
+                        <div style={{ cursor: "pointer", color: "var(--status-danger" }} onClick={onDelete}>
+                            <DeleteIcon />
+                        </div>
+                    )}
+                </>
+            }
+            footer={
+                <Flex flexDirection="row" style={{ gap: "0.2em" }}>
+                    {!!theme.homepageURL && <Link href={theme.homepageURL}>Homepage</Link>}
+                    {!!(theme.homepageURL && theme.supportURL) && " • "}
+                    {!!theme.supportURL && <Link href={theme.supportURL}>Support</Link>}
+                </Flex>
+            }
+        />
+    );
+}
+
+function OtherThemeCard({ theme, enabled, onChange, onDelete }: OtherThemeCardProps) {
     return (
         <AddonCard
             name={theme.name}
@@ -151,7 +220,7 @@ function ThemesTab() {
     const fileInputRef = useRef<HTMLInputElement>(null);
     const [currentTab, setCurrentTab] = useState(ThemeTab.LOCAL);
     const [themeText, setThemeText] = useState(settings.themeLinks.join("\n"));
-    const [userThemes, setUserThemes] = useState<UserThemeHeader[] | null>(null);
+    const [userThemes, setUserThemes] = useState<ThemeHeader[] | null>(null);
     const [themeDir, , themeDirPending] = useAwaiter(VencordNative.themes.getThemesDir);
 
     useEffect(() => {
@@ -160,7 +229,55 @@ function ThemesTab() {
 
     async function refreshLocalThemes() {
         const themes = await VencordNative.themes.getThemesList();
-        setUserThemes(themes);
+
+        const themeInfo: ThemeHeader[] = [];
+
+        for (const { fileName, content } of themes) {
+            if (!fileName.endsWith(".css")) continue;
+
+            if ((!IS_WEB || "armcord" in window) && fileName.endsWith(".user.css")) {
+                // handle it as usercss
+                const header = await usercssParse(content, fileName);
+
+                themeInfo.push({
+                    type: "usercss",
+                    header
+                });
+
+                Settings.userCssVars[header.id] ??= {};
+
+                for (const [name, varInfo] of Object.entries(header.vars ?? {})) {
+                    let normalizedValue = "";
+
+                    switch (varInfo.type) {
+                        case "text":
+                        case "color":
+                        case "checkbox":
+                            normalizedValue = varInfo.default;
+                            break;
+                        case "select":
+                            normalizedValue = varInfo.options.find(v => v.name === varInfo.default)!.value;
+                            break;
+                        case "range":
+                            normalizedValue = `${varInfo.default}${varInfo.units}`;
+                            break;
+                        case "number":
+                            normalizedValue = String(varInfo.default);
+                            break;
+                    }
+
+                    Settings.userCssVars[header.id][name] ??= normalizedValue;
+                }
+            } else {
+                // presumably BD but could also be plain css
+                themeInfo.push({
+                    type: "other",
+                    header: getThemeInfo(stripBOM(content), fileName)
+                });
+            }
+        }
+
+        setUserThemes(themeInfo);
     }
 
     // When a local theme is enabled/disabled, update the settings
@@ -269,19 +386,33 @@ function ThemesTab() {
                     </Card>
 
                     <div className={cl("grid")}>
-                        {userThemes?.map(theme => (
-                            <ThemeCard
-                                key={theme.fileName}
-                                enabled={settings.enabledThemes.includes(theme.fileName)}
-                                onChange={enabled => onLocalThemeChange(theme.fileName, enabled)}
-                                onDelete={async () => {
-                                    onLocalThemeChange(theme.fileName, false);
-                                    await VencordNative.themes.deleteTheme(theme.fileName);
-                                    refreshLocalThemes();
-                                }}
-                                theme={theme}
-                            />
-                        ))}
+                        {userThemes?.map(({ type, header: theme }: ThemeHeader) => (
+                            type === "other" ? (
+                                <OtherThemeCard
+                                    key={theme.fileName}
+                                    enabled={settings.enabledThemes.includes(theme.fileName)}
+                                    onChange={enabled => onLocalThemeChange(theme.fileName, enabled)}
+                                    onDelete={async () => {
+                                        onLocalThemeChange(theme.fileName, false);
+                                        await VencordNative.themes.deleteTheme(theme.fileName);
+                                        refreshLocalThemes();
+                                    }}
+                                    theme={theme as UserThemeHeader}
+                                />
+                            ) : (
+                                <UserCSSThemeCard
+                                    key={theme.fileName}
+                                    enabled={settings.enabledThemes.includes(theme.fileName)}
+                                    onChange={enabled => onLocalThemeChange(theme.fileName, enabled)}
+                                    onDelete={async () => {
+                                        onLocalThemeChange(theme.fileName, false);
+                                        await VencordNative.themes.deleteTheme(theme.fileName);
+                                        refreshLocalThemes();
+                                    }}
+                                    onSettingsReset={refreshLocalThemes}
+                                    theme={theme as UserstyleHeader}
+                                />
+                            )))}
                     </div>
                 </Forms.FormSection>
             </>

src/components/ThemeSettings/UserCSSModal.tsx

@@ -0,0 +1,205 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import { Settings, useSettings } from "@api/Settings";
+import { Flex } from "@components/Flex";
+import { CopyIcon, PasteIcon, ResetIcon } from "@components/Icons";
+import { copyWithToast } from "@utils/misc";
+import { ModalCloseButton, ModalContent, ModalHeader, ModalProps, ModalRoot } from "@utils/modal";
+import { showToast, Text, Toasts, Tooltip } from "@webpack/common";
+import { type ReactNode } from "react";
+import { UserstyleHeader } from "usercss-meta";
+
+import { SettingBooleanComponent, SettingColorComponent, SettingNumberComponent, SettingRangeComponent, SettingSelectComponent, SettingTextComponent } from "./components";
+
+interface UserCSSSettingsModalProps {
+    modalProps: ModalProps;
+    theme: UserstyleHeader;
+    onSettingsReset: () => void;
+}
+
+function ExportButton({ themeSettings }: { themeSettings: Settings["userCssVars"][""]; }) {
+    return <Tooltip text={"Copy theme settings"}>
+        {({ onMouseLeave, onMouseEnter }) => (
+            <div
+                style={{ cursor: "pointer" }}
+                onMouseEnter={onMouseEnter}
+                onMouseLeave={onMouseLeave}
+
+                onClick={() => {
+                    copyWithToast(JSON.stringify(themeSettings), "Copied theme settings to clipboard.");
+                }}>
+                <CopyIcon />
+            </div>
+        )}
+    </Tooltip>;
+}
+
+function ImportButton({ themeSettings }: { themeSettings: Settings["userCssVars"][""]; }) {
+    return <Tooltip text={"Paste theme settings"}>
+        {({ onMouseLeave, onMouseEnter }) => (
+            <div
+                style={{ cursor: "pointer" }}
+                onMouseEnter={onMouseEnter}
+                onMouseLeave={onMouseLeave}
+
+                onClick={async () => {
+                    const clip = (await navigator.clipboard.read())[0];
+
+                    if (!clip) return showToast("Your clipboard is empty.", Toasts.Type.FAILURE);
+
+                    if (!clip.types.includes("text/plain"))
+                        return showToast("Your clipboard doesn't have valid settings data.", Toasts.Type.FAILURE);
+
+                    try {
+                        var potentialSettings: Record<string, string> =
+                            JSON.parse(await clip.getType("text/plain").then(b => b.text()));
+                    } catch (e) {
+                        return showToast("Your clipboard doesn't have valid settings data.", Toasts.Type.FAILURE);
+                    }
+
+                    for (const [key, value] of Object.entries(potentialSettings)) {
+                        if (Object.prototype.hasOwnProperty.call(themeSettings, key))
+                            themeSettings[key] = value;
+                    }
+
+                    showToast("Pasted theme settings from clipboard.", Toasts.Type.SUCCESS);
+                }}>
+                <PasteIcon />
+            </div>
+        )}
+    </Tooltip>;
+}
+
+interface ResetButtonProps {
+    themeSettings: Settings["userCssVars"];
+    themeId: string;
+    close: () => Promise<void>;
+    onReset: () => void;
+}
+
+function ResetButton({ themeSettings, themeId, close, onReset }: ResetButtonProps) {
+    return <Tooltip text={"Reset settings to default"}>
+        {({ onMouseLeave, onMouseEnter }) => (
+            <div
+                style={{ cursor: "pointer" }}
+                onMouseEnter={onMouseEnter}
+                onMouseLeave={onMouseLeave}
+
+                onClick={async () => {
+                    await close(); // close the modal first to stop rendering
+                    delete themeSettings[themeId];
+                    onReset();
+                }}>
+                <ResetIcon />
+            </div>
+        )}
+    </Tooltip>;
+}
+
+export function UserCSSSettingsModal({ modalProps, theme, onSettingsReset }: UserCSSSettingsModalProps) {
+    // @ts-expect-error UseSettings<> can't determine this is a valid key
+    const { userCssVars } = useSettings(["userCssVars"], false);
+
+    const themeVars = userCssVars[theme.id];
+
+    const controls: ReactNode[] = [];
+
+    for (const [name, varInfo] of Object.entries(theme.vars)) {
+        switch (varInfo.type) {
+            case "text": {
+                controls.push(
+                    <SettingTextComponent
+                        label={varInfo.label}
+                        name={name}
+                        themeSettings={themeVars}
+                    />
+                );
+                break;
+            }
+
+            case "checkbox": {
+                controls.push(
+                    <SettingBooleanComponent
+                        label={varInfo.label}
+                        name={name}
+                        themeSettings={themeVars}
+                    />
+                );
+                break;
+            }
+
+            case "color": {
+                controls.push(
+                    <SettingColorComponent
+                        label={varInfo.label}
+                        name={name}
+                        themeSettings={themeVars}
+                    />
+                );
+                break;
+            }
+
+            case "number": {
+                controls.push(
+                    <SettingNumberComponent
+                        label={varInfo.label}
+                        name={name}
+                        themeSettings={themeVars}
+                    />
+                );
+                break;
+            }
+
+            case "select": {
+                controls.push(
+                    <SettingSelectComponent
+                        label={varInfo.label}
+                        name={name}
+                        options={varInfo.options}
+                        default={varInfo.default}
+                        themeSettings={themeVars}
+                    />
+                );
+                break;
+            }
+
+            case "range": {
+                controls.push(
+                    <SettingRangeComponent
+                        label={varInfo.label}
+                        name={name}
+                        default={varInfo.default}
+                        min={varInfo.min}
+                        max={varInfo.max}
+                        step={varInfo.step}
+                        themeSettings={themeVars}
+                    />
+                );
+                break;
+            }
+        }
+    }
+
+    return (
+        <ModalRoot {...modalProps}>
+            <ModalHeader separator={false}>
+                <Text variant="heading-lg/semibold" style={{ flexGrow: 1 }}>Settings for {theme.name}</Text>
+                <Flex style={{ gap: 4, marginRight: 4 }} className="vc-settings-usercss-ie-buttons">
+                    <ExportButton themeSettings={themeVars} />
+                    <ImportButton themeSettings={themeVars} />
+                    <ResetButton themeSettings={userCssVars} themeId={theme.id} close={modalProps.onClose} onReset={onSettingsReset} />
+                </Flex>
+                <ModalCloseButton onClick={modalProps.onClose} />
+            </ModalHeader>
+            <ModalContent>
+                <Flex flexDirection="column" style={{ gap: 12, marginBottom: 16 }}>
+                    {controls}
+                </Flex>
+            </ModalContent>
+        </ModalRoot>
+    );
+}

src/components/ThemeSettings/components/SettingBooleanComponent.tsx

@@ -0,0 +1,35 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import { Forms, Switch } from "@webpack/common";
+
+interface Props {
+    label: string;
+    name: string;
+    themeSettings: Record<string, string>;
+}
+
+export function SettingBooleanComponent({ label, name, themeSettings }: Props) {
+    function handleChange(value: boolean) {
+        const corrected = value ? "1" : "0";
+
+        themeSettings[name] = corrected;
+    }
+
+    return (
+        <Forms.FormSection>
+            <Switch
+                key={name}
+                value={themeSettings[name] === "1"}
+                onChange={handleChange}
+                hideBorder
+                style={{ marginBottom: "0.5em" }}
+            >
+                {label}
+            </Switch>
+        </Forms.FormSection>
+    );
+}

src/components/ThemeSettings/components/SettingColorComponent.tsx

@@ -0,0 +1,52 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import "./colorStyles.css";
+
+import { classNameFactory } from "@api/Styles";
+import { findByCodeLazy, findComponentByCodeLazy } from "@webpack";
+import { Forms, useMemo } from "@webpack/common";
+
+interface ColorPickerProps {
+    color: number | null;
+    showEyeDropper?: boolean;
+    onChange(value: number | null): void;
+}
+const ColorPicker = findComponentByCodeLazy<ColorPickerProps>(".Messages.USER_SETTINGS_PROFILE_COLOR_SELECT_COLOR", ".BACKGROUND_PRIMARY)");
+
+// TinyColor is completely unmangled and it's duplicated in two modules! Fun!
+const TinyColor: tinycolor.Constructor = findByCodeLazy("this._gradientType=");
+
+const cl = classNameFactory("vc-usercss-settings-color-");
+
+interface Props {
+    label: string;
+    name: string;
+    themeSettings: Record<string, string>;
+}
+
+export function SettingColorComponent({ label, name, themeSettings }: Props) {
+    function handleChange(value: number) {
+        const corrected = "#" + (value?.toString(16).padStart(6, "0") ?? "000000");
+
+        themeSettings[name] = corrected;
+    }
+
+    const normalizedValue = useMemo(() => parseInt(TinyColor(themeSettings[name]).toHex(), 16), [themeSettings[name]]);
+
+    return (
+        <Forms.FormSection>
+            <div className={cl("swatch-row")}>
+                <span>{label}</span>
+                <ColorPicker
+                    key={name}
+                    color={normalizedValue}
+                    onChange={handleChange}
+                />
+            </div>
+        </Forms.FormSection>
+    );
+}

src/components/ThemeSettings/components/SettingNumberComponent.tsx

@@ -0,0 +1,32 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import { Forms, TextInput } from "@webpack/common";
+
+interface Props {
+    label: string;
+    name: string;
+    themeSettings: Record<string, string>;
+}
+
+export function SettingNumberComponent({ label, name, themeSettings }: Props) {
+    function handleChange(value: string) {
+        themeSettings[name] = value;
+    }
+
+    return (
+        <Forms.FormSection>
+            <Forms.FormTitle tag="h5">{label}</Forms.FormTitle>
+            <TextInput
+                type="number"
+                pattern="-?[0-9]+"
+                key={name}
+                value={themeSettings[name]}
+                onChange={handleChange}
+            />
+        </Forms.FormSection>
+    );
+}

src/components/ThemeSettings/components/SettingRangeComponent.tsx

@@ -0,0 +1,52 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import { Forms, Slider, useMemo } from "@webpack/common";
+
+interface Props {
+    label: string;
+    name: string;
+    default: number;
+    min?: number;
+    max?: number;
+    step?: number;
+    themeSettings: Record<string, string>;
+}
+
+export function SettingRangeComponent({ label, name, default: def, min, max, step, themeSettings }: Props) {
+    function handleChange(value: number) {
+        const corrected = value.toString();
+
+        themeSettings[name] = corrected;
+    }
+
+    const markers = useMemo(() => {
+        const markers: number[] = [];
+
+        // defaults taken from https://github.com/openstyles/stylus/wiki/Writing-UserCSS#default-value
+        for (let i = (min ?? 0); i <= (max ?? 10); i += (step ?? 1)) {
+            markers.push(i);
+        }
+
+        return markers;
+    }, [min, max, step]);
+
+    return (
+        <Forms.FormSection>
+            <Forms.FormTitle tag="h5">{label}</Forms.FormTitle>
+            <Slider
+                initialValue={parseInt(themeSettings[name], 10)}
+                defaultValue={def}
+                onValueChange={handleChange}
+                minValue={min}
+                maxValue={max}
+
+                markers={markers}
+                stickToMarkers={true}
+            />
+        </Forms.FormSection>
+    );
+}

src/components/ThemeSettings/components/SettingSelectComponent.tsx

@@ -0,0 +1,51 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import { identity } from "@utils/misc";
+import { ComponentTypes, Forms, Select, useMemo } from "@webpack/common";
+
+interface Props {
+    label: string;
+    name: string;
+    options: {
+        name: string;
+        label: string;
+        value: string;
+    }[];
+    default: string;
+    themeSettings: Record<string, string>;
+}
+
+export function SettingSelectComponent({ label, name, options, default: def, themeSettings }: Props) {
+    function handleChange(value: string) {
+        themeSettings[name] = value;
+    }
+
+    const opts = useMemo(() => options.map(option => ({
+        disabled: false,
+
+        key: option.name,
+        value: option.value,
+        default: def === option.name,
+        label: option.label
+    } satisfies ComponentTypes.SelectOption)), [options, def]);
+
+    return (
+        <Forms.FormSection>
+            <Forms.FormTitle tag="h5">{label}</Forms.FormTitle>
+            <Select
+                placeholder={label}
+                key={name}
+                options={opts}
+                closeOnSelect={true}
+
+                select={handleChange}
+                isSelected={v => v === themeSettings[name]}
+                serialize={identity}
+            />
+        </Forms.FormSection>
+    );
+}

src/components/ThemeSettings/components/SettingTextComponent.tsx

@@ -0,0 +1,30 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import { Forms, TextInput } from "@webpack/common";
+
+interface Props {
+    label: string;
+    name: string;
+    themeSettings: Record<string, string>;
+}
+
+export function SettingTextComponent({ label, name, themeSettings }: Props) {
+    function handleChange(value: string) {
+        themeSettings[name] = value;
+    }
+
+    return (
+        <Forms.FormSection>
+            <Forms.FormTitle tag="h5">{label}</Forms.FormTitle>
+            <TextInput
+                key={name}
+                value={themeSettings[name]}
+                onChange={handleChange}
+            />
+        </Forms.FormSection>
+    );
+}

src/components/ThemeSettings/components/colorStyles.css

@@ -0,0 +1,19 @@
+.vc-usercss-settings-color-swatch-row {
+    display: flex;
+    flex-direction: row;
+    width: 100%;
+    align-items: center;
+}
+
+.vc-usercss-settings-color-swatch-row > span {
+    display: block;
+    flex: 1;
+    overflow: hidden;
+    margin-top: 0;
+    margin-bottom: 0;
+    color: var(--header-primary);
+    line-height: 24px;
+    font-size: 16px;
+    font-weight: 500;
+    word-wrap: break-word;
+}

src/components/ThemeSettings/components/index.ts

@@ -0,0 +1,12 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+export * from "./SettingBooleanComponent";
+export * from "./SettingColorComponent";
+export * from "./SettingNumberComponent";
+export * from "./SettingRangeComponent";
+export * from "./SettingSelectComponent";
+export * from "./SettingTextComponent";

src/components/ThemeSettings/themesStyles.css

@@ -27,3 +27,14 @@
 .vc-settings-theme-author::before {
     content: "by ";
 }
+
+.vc-settings-usercss-ie-buttons > div {
+    color: var(--interactive-normal);
+    opacity: .5;
+    padding: 4px;
+}
+
+.vc-settings-usercss-ie-buttons > div:hover {
+    color: var(--interactive-hover);
+    opacity: 1;
+}

src/components/VencordSettings/shared.tsx

@@ -17,7 +17,6 @@
 */
 
 import "./settingsStyles.css";
-import "./themesStyles.css";
 
 import ErrorBoundary from "@components/ErrorBoundary";
 import { handleComponentFailed } from "@components/handleComponentFailed";

src/main/ipcMain.ts

@@ -29,7 +29,6 @@ import { join, normalize } from "path";
 
 import monacoHtml from "~fileContent/monacoWin.html;base64";
 
-import { getThemeInfo, stripBOM, UserThemeHeader } from "./themes";
 import { ALLOWED_PROTOCOLS, QUICKCSS_PATH, SETTINGS_DIR, SETTINGS_FILE, THEMES_DIR } from "./utils/constants";
 import { makeLinksOpenExternally } from "./utils/externalLinks";
 
@@ -47,21 +46,11 @@ function readCss() {
     return readFile(QUICKCSS_PATH, "utf-8").catch(() => "");
 }
 
-async function listThemes(): Promise<UserThemeHeader[]> {
-    const files = await readdir(THEMES_DIR).catch(() => []);
-
-    const themeInfo: UserThemeHeader[] = [];
-
-    for (const fileName of files) {
-        if (!fileName.endsWith(".css")) continue;
-
-        const data = await getThemeData(fileName).then(stripBOM).catch(() => null);
-        if (data == null) continue;
-
-        themeInfo.push(getThemeInfo(data, fileName));
-    }
-
-    return themeInfo;
+function listThemes(): Promise<{ fileName: string; content: string; }[]> {
+    return readdir(THEMES_DIR)
+        .then(files =>
+            Promise.all(files.map(async fileName => ({ fileName, content: await getThemeData(fileName) }))))
+        .catch(() => []);
 }
 
 function getThemeData(fileName: string) {

src/plugins/_core/settings.tsx

@@ -101,7 +101,7 @@ export default definePlugin({
             {
                 section: "VencordThemes",
                 label: "Themes",
-                element: require("@components/VencordSettings/ThemesTab").default,
+                element: require("@components/ThemeSettings/ThemesTab").default,
                 className: "vc-themes"
             },
             !IS_UPDATER_DISABLED && {

src/utils/dependencies.ts

@@ -16,6 +16,9 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
+import type StylusRenderer = require("stylus/lib/renderer");
+import type LessStatic from "less";
+
 import { makeLazy } from "./lazy";
 import { EXTENSION_BASE_URL } from "./web-metadata";
 
@@ -84,3 +87,18 @@ export const shikiOnigasmSrc = "https://unpkg.com/@vap/shiki@0.10.3/dist/onig.wa
 
 // @ts-expect-error
 export const getStegCloak = /* #__PURE__*/ makeLazy(() => import("https://unpkg.com/stegcloak-dist@1.0.0/index.js"));
+
+export const getStylus = /* #__PURE__*/ makeLazy(async () => {
+    const stylusScript = await fetch("https://unpkg.com/stylus-lang-bundle@0.58.1/dist/stylus-renderer.min.js").then(r => r.text());
+    // the stylus bundle doesn't have a header that checks for export conditions so we can just patch the script to
+    // return the renderer itself
+    const patchedScript = stylusScript.replace("var StylusRenderer=", "return ");
+    return Function(patchedScript)() as typeof StylusRenderer;
+});
+
+export const getLess = /* #__PURE__*/ makeLazy(async () => {
+    const lessScript = await fetch("https://unpkg.com/less@4.2.0/dist/less.min.js").then(r => r.text());
+    const module = { exports: {} };
+    Function("module", "exports", lessScript)(module, module.exports);
+    return module.exports as LessStatic;
+});

src/utils/quickCss.ts

@@ -17,7 +17,12 @@
 */
 
 import { addSettingsListener, Settings } from "@api/Settings";
+import { Toasts } from "@webpack/common";
 
+import { Logger } from "./Logger";
+import { compileUsercss } from "./themes/usercss/compiler";
+
+const logger = new Logger("QuickCSS");
 
 let style: HTMLStyleElement;
 let themesStyle: HTMLStyleElement;
@@ -62,15 +67,69 @@ async function initThemes() {
     const links: string[] = [...themeLinks];
 
     if (IS_WEB) {
-        for (const theme of enabledThemes) {
-            const themeData = await VencordNative.themes.getThemeData(theme);
-            if (!themeData) continue;
+        // make copy so we can remove themes that are missing
+        for (let i = enabledThemes.length - 1; i >= 0; i--) {
+            const theme = enabledThemes[i];
+
+            try {
+                var themeData = await VencordNative.themes.getThemeData(theme);
+            } catch (e) {
+                logger.warn("Failed to get theme data for", theme, "(has it gone missing?)", e);
+            }
+
+            if (!themeData) {
+                // disable the theme since it has problems
+                Settings.enabledThemes = enabledThemes.splice(enabledThemes.indexOf(theme), 1);
+                continue;
+            }
+
             const blob = new Blob([themeData], { type: "text/css" });
             links.push(URL.createObjectURL(blob));
         }
     } else {
-        const localThemes = enabledThemes.map(theme => `vencord:///themes/${theme}?v=${Date.now()}`);
-        links.push(...localThemes);
+        for (let i = enabledThemes.length - 1; i >= 0; i--) {
+            const theme = enabledThemes[i];
+
+            if (theme.endsWith(".user.css")) continue;
+
+            try {
+                // whilst this is unnecessary here, we're doing it to make sure the theme is valid
+                await VencordNative.themes.getThemeData(theme);
+            } catch (e) {
+                logger.warn("Failed to get theme data for", theme, "(has it gone missing?)", e);
+                Settings.enabledThemes = enabledThemes.splice(enabledThemes.indexOf(theme), 1);
+                continue;
+            }
+
+            links.push(`vencord:///themes/${theme}?v=${Date.now()}`);
+        }
+    }
+
+    if (!IS_WEB || "armcord" in window) {
+        for (let i = enabledThemes.length - 1; i >= 0; i--) {
+            const theme = enabledThemes[i];
+
+            if (!theme.endsWith(".user.css")) continue;
+
+            // UserCSS goes through a compile step first
+            const css = await compileUsercss(theme);
+            if (!css) {
+                // let's not leave the user in the dark about this and point them to where they can find the error
+                Toasts.show({
+                    message: `Failed to compile ${theme}, check the console for more info.`,
+                    type: Toasts.Type.FAILURE,
+                    id: Toasts.genId(),
+                    options: {
+                        position: Toasts.Position.BOTTOM
+                    }
+                });
+                Settings.enabledThemes = enabledThemes.splice(enabledThemes.indexOf(theme), 1);
+                continue;
+            }
+
+            const blob = new Blob([css], { type: "text/css" });
+            links.push(URL.createObjectURL(blob));
+        }
     }
 
     themesStyle.textContent = links.map(link => `@import url("${link.trim()}");`).join("\n");
@@ -85,6 +144,7 @@ document.addEventListener("DOMContentLoaded", () => {
 
     addSettingsListener("themeLinks", initThemes);
     addSettingsListener("enabledThemes", initThemes);
+    addSettingsListener("userCssVars", initThemes, false);
 
     if (!IS_WEB)
         VencordNative.quickCss.addThemeChangeListener(initThemes);

src/utils/themes/index.ts

@@ -0,0 +1,17 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import type { UserstyleHeader } from "usercss-meta";
+
+import type { UserThemeHeader } from "./bd";
+
+export type ThemeHeader = {
+    type: "other";
+    header: UserThemeHeader;
+} | {
+    type: "usercss";
+    header: UserstyleHeader;
+};

src/utils/themes/usercss/compiler.ts

@@ -0,0 +1,115 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import { Settings } from "@api/Settings";
+import { getLess, getStylus } from "@utils/dependencies";
+import { Logger } from "@utils/Logger";
+
+import { usercssParse } from ".";
+
+const UserCSSLogger = new Logger("UserCSS:Compiler", "#d2acf5");
+
+const preprocessors: { [preprocessor: string]: (text: string, vars: Record<string, string>) => Promise<string>; } = {
+    async default(text: string, vars: Record<string, string>) {
+        const variables = Object.entries(vars)
+            .map(([name, value]) => `--${name}: ${value}`)
+            .join("; ");
+
+        return `/* ==Vencord== */\n:root{${variables}}\n/* ==/Vencord== */${text}`;
+    },
+
+    async uso(text: string, vars: Record<string, string>) {
+        for (const [k, v] of Object.entries(vars)) {
+            text = text.replace(new RegExp(`\\/\\*\\[\\[${k}\\]\\]\\*\\/`, "g"), v);
+        }
+
+        return text;
+    },
+
+    async stylus(text: string, vars: Record<string, string>) {
+        const StylusRenderer = await getStylus();
+
+        const variables = Object.entries(vars)
+            .map(([name, value]) => `${name} = ${value}`)
+            .join("\n");
+
+        const stylusDoc = `// ==Vencord==\n${variables}\n// ==/Vencord==\n${text}`;
+
+        return new StylusRenderer(stylusDoc).render();
+    },
+
+    async less(text: string, vars: Record<string, string>) {
+        const less = await getLess();
+
+        const variables = Object.entries(vars)
+            .map(([name, value]) => `@${name}: ${value};`)
+            .join("\n");
+
+        const lessDoc = `// ==Vencord==\n${variables}\n// ==/Vencord==\n${text}`;
+
+        return less.render(lessDoc).then(r => r.css);
+    }
+};
+
+export async function compileUsercss(fileName: string) {
+    try {
+        var themeData = await VencordNative.themes.getThemeData(fileName);
+    } catch (e) {
+        UserCSSLogger.warn("Failed to get theme data for", fileName, "(has it gone missing?)", e);
+    }
+    if (!themeData) return null;
+
+    // UserCSS preprocessor order look like this:
+    // - use the preprocessor defined
+    // - if variables are set, `uso`
+    // - otherwise, `default`
+    const { vars = {}, preprocessor = Object.keys(vars).length > 0 ? "uso" : "default", id } = await usercssParse(themeData, fileName);
+
+    const preprocessorFn = preprocessors[preprocessor];
+
+    if (!preprocessorFn) {
+        UserCSSLogger.error("File", fileName, "requires preprocessor", preprocessor, "which isn't known to Vencord");
+        return null;
+    }
+
+    const varsToPass = {
+        vencord: "true"
+    };
+
+    for (const [k, v] of Object.entries(vars)) {
+        varsToPass[k] = Settings.userCssVars[id]?.[k] ?? v.default;
+
+        switch (v.type) {
+            case "checkbox": {
+                if (["less", "stylus"].includes(preprocessor)) {
+                    varsToPass[k] = varsToPass[k] === "1" ? "true" : "false";
+                }
+                break;
+            }
+
+            case "range": {
+                varsToPass[k] = `${varsToPass[k]}${v.units ?? "px"}`;
+                break;
+            }
+
+            case "text": {
+                if (preprocessor === "stylus") {
+                    varsToPass[k] = `"${varsToPass[k].replace(/"/g, "\" + '\"' + \"")}"`;
+                } else {
+                    varsToPass[k] = `"${varsToPass[k].replace(/\//g, "\\\\").replace(/"/g, '\\"')}"`;
+                }
+                break;
+            }
+        }
+    }
+
+    try {
+        return await preprocessorFn(themeData, varsToPass);
+    } catch (error) {
+        UserCSSLogger.error("File", fileName, "failed to compile with preprocessor", preprocessor, error);
+        return null;
+    }
+}

src/utils/themes/usercss/index.ts

@@ -0,0 +1,44 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import { Logger } from "@utils/Logger";
+import { parse as originalParse, UserstyleHeader } from "usercss-meta";
+
+const UserCSSLogger = new Logger("UserCSS", "#d2acf5");
+
+export async function usercssParse(text: string, fileName: string): Promise<UserstyleHeader> {
+    const { metadata, errors } = originalParse(text.replace(/\r/g, ""), {
+        allowErrors: true,
+        unknownKey: "assign"
+    });
+
+    if (errors.length) {
+        UserCSSLogger.warn("Parsed", fileName, "with errors:", errors);
+    }
+
+    const requiredPlugins = metadata["vc-requiredPlugins"]?.split(",").map(p => p.trim());
+
+    return {
+        ...metadata,
+        fileName,
+        id: await getUserCssId(metadata),
+        requiredPlugins
+    };
+}
+
+export async function getUserCssId(header: UserstyleHeader): Promise<string> {
+    const encoder = new TextEncoder();
+
+    const nameBuf = encoder.encode(header.name);
+    const namespaceBuf = encoder.encode(header.namespace);
+
+    const nameHash = new Uint8Array(await window.crypto.subtle.digest("SHA-256", nameBuf));
+    const namespaceHash = new Uint8Array(await window.crypto.subtle.digest("SHA-256", namespaceBuf));
+
+    const idHash = await window.crypto.subtle.digest("SHA-256", new Uint8Array([...nameHash, ...namespaceHash]));
+
+    return window.btoa(String.fromCharCode(...new Uint8Array(idHash))).substring(0, 43); // base64 adds one more padding character
+}

src/utils/themes/usercss/usercss-meta.d.ts

@@ -0,0 +1,134 @@
+/*
+ * Vencord, a Discord client mod
+ * Copyright (c) 2023 Vendicated and contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+declare module "usercss-meta" {
+    import { Simplify } from "type-fest";
+
+    export type UserCSSVariable = Simplify<{ name: string; label: string; } & (
+        | {
+            type: "text";
+            default: string;
+        }
+        | {
+            type: "color";
+            // Hex, rgb(), rgba()
+            default: string;
+        }
+        | {
+            type: "checkbox";
+            default: string;
+        }
+        | {
+            type: "range";
+            default: number;
+            min?: number;
+            max?: number;
+            step?: number;
+            units?: string;
+        }
+        | {
+            type: "number";
+            default: number;
+        }
+        | {
+            type: "select";
+            default: string;
+            options: { name: string; label: string; value: string; }[];
+        }
+    )>;
+
+    export interface UserstyleHeader {
+        /**
+         * The unique ID of the UserCSS style.
+         *
+         * @vencord Specific to Vencord, not part of the original module.
+         */
+        id: string;
+
+        /**
+         * The file name of the UserCSS style.
+         *
+         * @vencord Specific to Vencord, not part of the original module.
+         */
+        fileName: string;
+
+        /**
+         * The required plugins for this style.
+         *
+         * @vencord Specific to Vencord, not part of the original module.
+         * @see {@link vc-requiredPlugins}
+         */
+        requiredPlugins?: string[];
+
+        /**
+         * The name of your style.
+         *
+         * The combination of {@link name} and {@link namespace} must be unique.
+         */
+        name: string;
+        /**
+         * The namespace of the style. Helps to distinguish between styles with the same name.
+         *
+         * The combination of {@link name} and {@link namespace} must be unique.
+         */
+        namespace: string;
+        /**
+         * The version of your style.
+         */
+        version: string;
+
+        /**
+         * A short significant description.
+         */
+        description?: string;
+        /**
+         * The author of the style.
+         */
+        author?: string;
+        /**
+         * The project's homepage.
+         *
+         * This is not an update URL. See {@link updateURL}.
+         */
+        homepageURL?: string;
+        /**
+         * The URL the user can report issues to the style author.
+         */
+        supportURL?: string;
+        /**
+         * The URL used when updating the style.
+         */
+        updateURL?: string;
+        /**
+         * The SPDX license identifier for this style. If none is included, the style is assumed to be All Rights Reserved.
+         */
+        license?: string;
+        /**
+         * The CSS preprocessor used to write this style.
+         */
+        preprocessor?: "default" | "uso" | "less" | "stylus";
+
+        /**
+         * A list of variables the style defines.
+         */
+        vars: Record<string, UserCSSVariable>;
+
+        /**
+         * Required plugins for this style to work. Comma-separated list of plugin names.
+         *
+         * @vencord This is a Vencord-specific extension, however we wish for this to become a standard for client mods
+         *          to implement, hence the more generic namespaced name.
+         */
+        "vc-requiredPlugins"?: string;
+    }
+
+    type UserCSSParseOptions = {
+        allowErrors: boolean;
+        unknownKey: "assign";
+    };
+
+    export function parse(text: string, options: UserCSSParseOptions): { metadata: UserstyleHeader; errors: { code: string; args: any; }[]; };
+}

src/webpack/common/types/components.d.ts

@@ -191,7 +191,7 @@ export type TextArea = ComponentType<PropsWithRef<Omit<HTMLProps<HTMLTextAreaEle
     onChange(v: string): void;
 }>>;
 
-interface SelectOption {
+export interface SelectOption {
     disabled?: boolean;
     value: any;
     label: string;