diff --git a/borlander/content.js b/borlander/content.js
index 1eef395..f09292f 100644
--- a/borlander/content.js
+++ b/borlander/content.js
@@ -1,51 +1,79 @@
 const domain = window.location.hostname;
 
-chrome.storage.local.get([domain, `${domain}_mode`], (result) => {
-    if (result[domain] === 'disabled') return;
+async function loadThemesRegistry() {
+    try {
+        const url = chrome.runtime.getURL('themes.json');
+        const res = await fetch(url);
+        if (!res.ok) throw new Error(`Failed to load themes.json: ${res.status}`);
+        return await res.json();
+    } catch (e) {
+        console.warn('Borlander: could not load themes registry, falling back to static theme', e);
+        return { themes: [] };
+    }
+}
 
-    const forceGlobal = result[`${domain}_mode`] === 'global';
-    let siteMatched = false;
+function themeAppliesToPage(theme) {
+    if (!theme) return false;
 
-    if (!forceGlobal) {
-
-        // 1. SONARR
-        const isSonarr = getComputedStyle(document.documentElement).getPropertyValue('--sonarrBlue').trim() !== "" ||
-            document.title.toLowerCase().includes('sonarr');
-        if (isSonarr) { injectSiteStyle('sites/sonarr.local/styles.css'); siteMatched = true; }
-
-        // 2. CHESS.COM
-        if (!siteMatched && (domain.includes('chess.com') || !!document.querySelector('.board-layout-main'))) {
-            injectSiteStyle('sites/chess.com/styles.css'); siteMatched = true;
-        }
-
-        // 3. ANILIST
-        if (!siteMatched && domain.includes('anilist.co')) {
-            injectSiteStyle('sites/anilist.co/styles.css'); siteMatched = true;
-        }
-
-        // 4. GITEA
-        if (!siteMatched && (!!document.querySelector('meta[content*="gitea"]') || domain.includes('gitea'))) {
-            injectSiteStyle('sites/gitea.local/styles.css'); siteMatched = true;
-        }
-
-        // 5. GITHUB
-        if (!siteMatched && domain.includes('github.com')) {
-            injectSiteStyle('sites/github.com/styles.css'); siteMatched = true;
-        }
-
-        if (!siteMatched && domain.includes('solana.com')) {
-            injectSiteStyle('sites/solana.com/styles.css'); siteMatched = true;
-        }
-
-        if (!siteMatched && domain.includes('chatgpt.com')) {
-            injectSiteStyle('sites/chatgpt.com/styles.css'); siteMatched = true;
-        }
+    if (theme.type === 'hostname') {
+        return typeof theme.hostnameIncludes === 'string' && domain.includes(theme.hostnameIncludes);
     }
 
-    if (!siteMatched) {
+    if (theme.type === 'heuristic' && theme.detect) {
+        const d = theme.detect;
+        let ok = false;
+
+        if (typeof d.hostnameIncludes === 'string') {
+            ok = ok || domain.includes(d.hostnameIncludes);
+        }
+        if (typeof d.titleIncludes === 'string') {
+            ok = ok || document.title.toLowerCase().includes(d.titleIncludes.toLowerCase());
+        }
+        if (typeof d.metaContentIncludes === 'string') {
+            ok = ok || !!document.querySelector(`meta[content*="${CSS.escape(d.metaContentIncludes)}"]`);
+        }
+        if (typeof d.cssVarNonEmpty === 'string') {
+            ok = ok || getComputedStyle(document.documentElement)
+                .getPropertyValue(d.cssVarNonEmpty)
+                .trim() !== '';
+        }
+
+        return ok;
+    }
+
+    return false;
+}
+
+function pickBestSiteTheme(themes) {
+    // Prefer hostname matches first, then heuristics.
+    for (const t of themes) {
+        if (t.type === 'hostname' && themeAppliesToPage(t)) return t;
+    }
+    for (const t of themes) {
+        if (t.type === 'heuristic' && themeAppliesToPage(t)) return t;
+    }
+    return null;
+}
+
+(async () => {
+    const registry = await loadThemesRegistry();
+    const themes = Array.isArray(registry.themes) ? registry.themes : [];
+    const applicable = pickBestSiteTheme(themes);
+
+    chrome.storage.local.get([domain, `${domain}_mode`], (result) => {
+        if (result[domain] === 'disabled') return;
+
+        // historical value is "global"; treat as "static".
+        const forceStatic = result[`${domain}_mode`] === 'global' || result[`${domain}_mode`] === 'static';
+
+        if (!forceStatic && applicable?.cssPath) {
+            injectSiteStyle(applicable.cssPath);
+            return;
+        }
+
         injectSiteStyle('styles.css');
-    }
-});
+    });
+})();
 
 function injectSiteStyle(path) {
     const link = document.createElement('link');
diff --git a/borlander/manifest.json b/borlander/manifest.json
index 431428a..ab821b9 100644
--- a/borlander/manifest.json
+++ b/borlander/manifest.json
@@ -32,13 +32,8 @@
         {
             "resources": [
                 "styles.css",
-                "sites/sonarr.local/styles.css",
-                "sites/chess.com/styles.css",
-                "sites/gitea.local/styles.css",
-                "sites/anilist.co/styles.css",
-                "sites/github.com/styles.css",
-                "sites/solana.com/styles.css",
-                "sites/chatgpt.com/styles.css"
+                "themes.json",
+                "sites/*/styles.css"
             ],
             "matches": [
                 "<all_urls>"
diff --git a/borlander/popup.js b/borlander/popup.js
index d5ab798..30e5c8d 100644
--- a/borlander/popup.js
+++ b/borlander/popup.js
@@ -1,3 +1,15 @@
+async function loadThemesRegistry() {
+    try {
+        const url = chrome.runtime.getURL('themes.json');
+        const res = await fetch(url);
+        if (!res.ok) throw new Error(`Failed to load themes.json: ${res.status}`);
+        return await res.json();
+    } catch (e) {
+        console.warn('Borlander: could not load themes registry', e);
+        return { themes: [] };
+    }
+}
+
 chrome.tabs.query({ active: true, currentWindow: true }, async (tabs) => {
     if (!tabs[0] || !tabs[0].url) return;
 
@@ -9,34 +21,69 @@ chrome.tabs.query({ active: true, currentWindow: true }, async (tabs) => {
     const btn = document.getElementById('toggle-btn');
     const themeBtn = document.getElementById('theme-mode-btn');
 
-    let hasSpecificTheme = false;
+    const registry = await loadThemesRegistry();
+    const themes = Array.isArray(registry.themes) ? registry.themes : [];
 
+    let hasSpecificTheme = false;
     try {
-        // Run detection logic inside the tab to match content.js logic
+        // Detect using the same rules as content.js, but executed within the actual page.
         const detectionResult = await chrome.scripting.executeScript({
             target: { tabId: activeTab.id },
-            func: () => {
+            args: [themes],
+            func: (themesFromExtension) => {
                 const domain = window.location.hostname;
-                const isSonarr = getComputedStyle(document.documentElement).getPropertyValue('--sonarrBlue').trim() !== "" ||
-                    document.title.toLowerCase().includes('sonarr');
-                const isChess = domain.includes('chess.com') || !!document.querySelector('.board-layout-main');
-                const isAnilist = domain.includes('anilist.co');
-                const isGitea = !!document.querySelector('meta[content*="gitea"]') || domain.includes('gitea');
-                const isGithub = domain.includes('github.com');
-                const isSolana = domain.includes('solana.com');
-                const isChatgpt = domain.includes('chatgpt.com');
 
-                return isSonarr || isChess || isSolana || isAnilist || isChatgpt || isGitea || isGithub;
+                function themeApplies(theme) {
+                    if (!theme) return false;
+
+                    if (theme.type === 'hostname') {
+                        return typeof theme.hostnameIncludes === 'string' && domain.includes(theme.hostnameIncludes);
+                    }
+
+                    if (theme.type === 'heuristic' && theme.detect) {
+                        const d = theme.detect;
+                        let ok = false;
+
+                        if (typeof d.hostnameIncludes === 'string') {
+                            ok = ok || domain.includes(d.hostnameIncludes);
+                        }
+                        if (typeof d.titleIncludes === 'string') {
+                            ok = ok || document.title.toLowerCase().includes(d.titleIncludes.toLowerCase());
+                        }
+                        if (typeof d.metaContentIncludes === 'string') {
+                            ok = ok || !!document.querySelector(`meta[content*="${CSS.escape(d.metaContentIncludes)}"]`);
+                        }
+                        if (typeof d.cssVarNonEmpty === 'string') {
+                            ok = ok || getComputedStyle(document.documentElement)
+                                .getPropertyValue(d.cssVarNonEmpty)
+                                .trim() !== '';
+                        }
+
+                        return ok;
+                    }
+
+                    return false;
+                }
+
+                // Prefer hostname rules, then heuristics.
+                for (const t of themesFromExtension) {
+                    if (t.type === 'hostname' && themeApplies(t)) return true;
+                }
+                for (const t of themesFromExtension) {
+                    if (t.type === 'heuristic' && themeApplies(t)) return true;
+                }
+
+                return false;
             }
         });
         hasSpecificTheme = detectionResult[0]?.result || false;
     } catch (e) {
-        console.warn("Could not inspect page for site-specific theme:", e);
+        console.warn('Could not inspect page for site-specific theme:', e);
     }
 
     chrome.storage.local.get([domain, `${domain}_mode`], (result) => {
         const isDisabled = result[domain] === 'disabled';
-        btn.textContent = isDisabled ? "Enable" : "Disable";
+        btn.textContent = isDisabled ? 'Enable' : 'Disable';
 
         btn.onclick = () => {
             if (isDisabled) chrome.storage.local.remove(domain);
@@ -47,15 +94,17 @@ chrome.tabs.query({ active: true, currentWindow: true }, async (tabs) => {
 
         if (hasSpecificTheme && !isDisabled) {
             themeBtn.style.display = 'block';
-            const isGlobalMode = result[`${domain}_mode`] === 'global';
-            themeBtn.textContent = isGlobalMode ? "Site Theme" : "Static Theme";
+            const isStaticMode = result[`${domain}_mode`] === 'global' || result[`${domain}_mode`] === 'static';
+            themeBtn.textContent = isStaticMode ? 'Site Theme' : 'Static Theme';
 
             themeBtn.onclick = () => {
-                const newMode = isGlobalMode ? 'site' : 'global';
+                const newMode = isStaticMode ? 'site' : 'static';
                 chrome.storage.local.set({ [`${domain}_mode`]: newMode });
                 chrome.tabs.reload(activeTab.id);
                 window.close();
             };
+        } else {
+            themeBtn.style.display = 'none';
         }
     });
 });
\ No newline at end of file
diff --git a/borlander/scripts/generate-themes.mjs b/borlander/scripts/generate-themes.mjs
new file mode 100644
index 0000000..fb9c5e8
--- /dev/null
+++ b/borlander/scripts/generate-themes.mjs
@@ -0,0 +1,79 @@
+import fs from 'node:fs/promises';
+import path from 'node:path';
+
+const ROOT = path.resolve(process.argv[2] ?? path.join(process.cwd(), 'borlander'));
+const SITES_DIR = path.join(ROOT, 'sites');
+const OUT_FILE = path.join(ROOT, 'themes.json');
+
+/**
+ * Heuristics for themes that don't map 1:1 to a hostname.
+ * Keyed by folder name under sites/.
+ */
+const HEURISTICS = {
+    'sonarr.local': {
+        type: 'heuristic',
+        detect: {
+            titleIncludes: 'sonarr',
+            cssVarNonEmpty: '--sonarrBlue'
+        }
+    },
+    'gitea.local': {
+        type: 'heuristic',
+        detect: {
+            metaContentIncludes: 'gitea',
+            hostnameIncludes: 'gitea'
+        }
+    }
+};
+
+const HOSTNAME_ALIASES = {
+    // folderName: hostnameIncludes
+    'web.whatsapp.com': 'web.whatsapp.com'
+};
+
+async function fileExists(p) {
+    try {
+        await fs.access(p);
+        return true;
+    } catch {
+        return false;
+    }
+}
+
+const entries = [];
+const siteFolders = (await fs.readdir(SITES_DIR, { withFileTypes: true }))
+    .filter((d) => d.isDirectory())
+    .map((d) => d.name)
+    .sort();
+
+for (const folder of siteFolders) {
+    const cssPath = path.join(SITES_DIR, folder, 'styles.css');
+    if (!(await fileExists(cssPath))) continue;
+
+    const relCssPath = `sites/${folder}/styles.css`;
+
+    if (HEURISTICS[folder]) {
+        entries.push({
+            id: folder,
+            cssPath: relCssPath,
+            ...HEURISTICS[folder]
+        });
+        continue;
+    }
+
+    const hostnameIncludes = HOSTNAME_ALIASES[folder] ?? folder;
+    entries.push({
+        id: folder,
+        type: 'hostname',
+        hostnameIncludes,
+        cssPath: relCssPath
+    });
+}
+
+const payload = {
+    version: 1,
+    themes: entries
+};
+
+await fs.writeFile(OUT_FILE, JSON.stringify(payload, null, 2) + '\n', 'utf8');
+console.log(`Wrote ${entries.length} themes to ${path.relative(process.cwd(), OUT_FILE)}`);
diff --git a/borlander/sites/music.youtube.com/styles.css b/borlander/sites/music.youtube.com/styles.css
new file mode 100644
index 0000000..e892d4a
--- /dev/null
+++ b/borlander/sites/music.youtube.com/styles.css
@@ -0,0 +1,16 @@
+#sections {
+    background-color: #000064 !important;
+}
+
+#left-content {
+    background-color: #000064 !important;
+}
+
+.background-gradient {
+    background-image: none !important;
+    background-color: #0000A4 !important;
+}
+
+:root {
+    --ytmusic-nav-bar: #000064 !important;
+}
\ No newline at end of file
diff --git a/borlander/sites/web.whatsapp.com/styles.css b/borlander/sites/web.whatsapp.com/styles.css
new file mode 100644
index 0000000..301cd16
--- /dev/null
+++ b/borlander/sites/web.whatsapp.com/styles.css
@@ -0,0 +1,26 @@
+#main,
+#side {
+    background-color: #0000A4;
+}
+
+#side>div {
+    background-color: #000064 !important;
+}
+
+header,
+#pane-side {
+    background-color: #000064 !important;
+}
+
+.xa3rncp.xa3rncp,
+.xa3rncp.xa3rncp:root {
+    --WDS-surface-default: #000064 !important;
+}
+
+:root {
+    --background-default: #000080 !important;
+}
+
+._ak72 {
+    background-color: #000080 !important;
+}
\ No newline at end of file
diff --git a/borlander/themes.json b/borlander/themes.json
new file mode 100644
index 0000000..c6c905d
--- /dev/null
+++ b/borlander/themes.json
@@ -0,0 +1,65 @@
+{
+  "version": 1,
+  "themes": [
+    {
+      "id": "anilist.co",
+      "type": "hostname",
+      "hostnameIncludes": "anilist.co",
+      "cssPath": "sites/anilist.co/styles.css"
+    },
+    {
+      "id": "chatgpt.com",
+      "type": "hostname",
+      "hostnameIncludes": "chatgpt.com",
+      "cssPath": "sites/chatgpt.com/styles.css"
+    },
+    {
+      "id": "chess.com",
+      "type": "hostname",
+      "hostnameIncludes": "chess.com",
+      "cssPath": "sites/chess.com/styles.css"
+    },
+    {
+      "id": "gitea.local",
+      "cssPath": "sites/gitea.local/styles.css",
+      "type": "heuristic",
+      "detect": {
+        "metaContentIncludes": "gitea",
+        "hostnameIncludes": "gitea"
+      }
+    },
+    {
+      "id": "github.com",
+      "type": "hostname",
+      "hostnameIncludes": "github.com",
+      "cssPath": "sites/github.com/styles.css"
+    },
+    {
+      "id": "music.youtube.com",
+      "type": "hostname",
+      "hostnameIncludes": "music.youtube.com",
+      "cssPath": "sites/music.youtube.com/styles.css"
+    },
+    {
+      "id": "solana.com",
+      "type": "hostname",
+      "hostnameIncludes": "solana.com",
+      "cssPath": "sites/solana.com/styles.css"
+    },
+    {
+      "id": "sonarr.local",
+      "cssPath": "sites/sonarr.local/styles.css",
+      "type": "heuristic",
+      "detect": {
+        "titleIncludes": "sonarr",
+        "cssVarNonEmpty": "--sonarrBlue"
+      }
+    },
+    {
+      "id": "web.whatsapp.com",
+      "type": "hostname",
+      "hostnameIncludes": "web.whatsapp.com",
+      "cssPath": "sites/web.whatsapp.com/styles.css"
+    }
+  ]
+}
diff --git a/readme.md b/readme.md
index ee429a7..3a2fe73 100644
--- a/readme.md
+++ b/readme.md
@@ -1,5 +1,24 @@
 # Borlander
 
+Borlander is a MV3 browser extension that applies a classic Borland blue/yellow theme globally, with optional site-specific overrides.
+
+## Site-specific themes (automatic)
+
+Any folder under `borlander/sites/<site>/styles.css` is treated as a site theme automatically.
+
+* If the folder name looks like a hostname (e.g. `github.com`), it matches when the current page hostname includes that string.
+* A couple themes are **heuristic-based** (currently `sonarr.local`, `gitea.local`) because they may run on custom domains. Those are defined in `borlander/scripts/generate-themes.mjs`.
+
+The registry lives in `borlander/themes.json` and is loaded by both `content.js` and `popup.js`.
+
+### Regenerate `themes.json`
+
+If you add/remove site themes in `borlander/sites/`, re-generate the registry:
+
+```fish
+node borlander/scripts/generate-themes.mjs
+```
+
 
 #### Monkeytype theme