fix: Fixed window controls not being accessible on fullscreen when element separation is 0, b=(no-bug), c=tabs

Author: mr-cheffy

src/zen/tabs/zen-tabs/vertical-tabs-topbar.inc.css

@@ -16,7 +16,8 @@ z-index: 1;
 
   &:not([zen-has-hover='true']):not([has-popup-menu]):not(:focus-within):not(:has(*:is([panelopen='true'], [open='true']))) {
     transition-delay: 0.2s;
-    height: var(--zen-element-separation);
+    /* In order to still use it on fullscreen, even if it's 0px, add .1px (almost invisible) */
+    height: calc(var(--zen-element-separation) + 0.1px);
     overflow: hidden;
     opacity: 0;
     & > * {