fix: adjust fullscreen behavior for vertical tabs to improve visibility and interaction

src/browser/base/content/zen-styles/zen-tabs/vertical-tabs-topbar.inc.css

@@ -4,10 +4,6 @@ height: var(--zen-toolbar-height);
   & {
     transition: height 0.2s ease-out, opacity 0.2s ease-out;
     transition-delay: 0.05s;
-
-    :root[inDOMFullscreen='true'] & {
-      max-height: 0;
-    }
   }
 
   &:not([zen-has-hover='true']):not([has-popup-menu]):not(:focus-within) {
@@ -20,3 +16,10 @@ height: var(--zen-toolbar-height);
     }
   }
 }
+
+:root[inDOMFullscreen='true'] & {
+  max-height: 0;
+  min-height: unset !important;
+  opacity: 0;
+  pointer-events: none;
+}

src/browser/base/content/zen-styles/zen-tabs/vertical-tabs.css

@@ -155,8 +155,8 @@
     }
 
     /* We enable this trick IF we follow any of theses conditions:
-      * - We are on a Mac
-      * - We are on a Linux with reversed CSD
+      * - We are supposed to hide the window controls (e.g. left sidebar, windows like layouts)
+      *    - This also involves linux's reverse GTK window controls, we'll need to handle that a bit differently
       * - If we are not in any of the above, we can still enable it if the user has bookmarks toolbar enabled
       */
     &:has(#PersonalToolbar[collapsed='false']) {