Fix mobile sidebar closed state

Author: ootakazuhiko

docs/assets/css/mobile-responsive.css

@@ -50,7 +50,14 @@
     border-right: 1px solid var(--border-color);
     box-shadow: 2px 0 8px rgba(0, 0, 0, 0.15);
     z-index: 1000;
-    transform: translateX(-100%);
+    /*
+     * main.css imports this file before declaring the default desktop sidebar
+     * transform. Keep the closed drawer state important so the later desktop
+     * `transform: translateX(0)` rule cannot leave the TOC covering content
+     * on mobile and tablet widths. The checked/open rule below is more
+     * specific and also important, so the menu button still opens it.
+     */
+    transform: translateX(-100%) !important;
     transition: transform 0.3s ease;
   }