chore(css): ensure css are not using direct colors

.github/workflows/ci.yml

@@ -32,6 +32,8 @@ jobs:
             frontend:
               - 'static/**'
               - 'biome.json'
+              - '.grit'
+              - '.stylelintrc.json'
               - 'jsconfig.json'
             backend:
               - 'src/**'
@@ -39,7 +41,7 @@ jobs:
               - 'Cargo.lock'
 
   frontend-linter:
-    name: Frontend — Biome
+    name: Frontend — CSS and JS checks (format, lint, rules, etc)
     needs: changes
     if: needs.changes.outputs.frontend == 'true'
     runs-on: ubuntu-latest
@@ -52,6 +54,14 @@ jobs:
       - name: Run Biome check
         run: biome ci static/
 
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 25
+
+      - name: Run Stylelint
+        run: npx stylelint "**/*.{css,scss}"
+
   rust-fmt:
     name: Rustfmt
     needs: changes

.stylelintrc.json

@@ -0,0 +1,27 @@
+{
+  "rules": {
+    "color-no-hex": true,
+    "color-named": "never",
+    "function-disallowed-list": ["rgb", "rgba", "hsl", "hsla", "hwb", "oklch", "oklab"],
+    "selector-disallowed-list": ["/\\[data-theme/"]
+  },
+  "overrides": [
+    {
+      "files": ["**/variables.css"],
+      "rules": {
+        "color-no-hex": null,
+        "color-named": null,
+        "function-disallowed-list": null
+      }
+    },
+    {
+      "files": ["**/themes/dark.css"],
+      "rules": {
+        "color-no-hex": null,
+        "color-named": null,
+        "function-disallowed-list": null,
+        "selector-disallowed-list": null
+      }
+    }
+  ]
+}