no-bug: Simplify stylings

src/zen/common/styles/zen-browser-ui.css

@@ -20,9 +20,13 @@ body,
   position: inherit;
 }
 
-:root:is([inDOMFullscreen="true"], [chromehidden~="location"], [chromehidden~="toolbar"]) {
+:root:is(
+  [inDOMFullscreen="true"], [chromehidden~="location"], 
+  [chromehidden~="toolbar"], [zen-little-window="true"]
+) {
   #navigator-toolbox,
-  #zen-sidebar-splitter {
+  #zen-sidebar-splitter,
+  #zen-sidebar-top-buttons {
     visibility: collapse;
   }
 }

src/zen/little-window/zen-little-window.css

@@ -9,15 +9,9 @@
  */
 
 :root[zen-little-window="true"] {
-  /*
-   * The navigator toolbox (sidebar + tab strip) and its splitter are
-   * never visible in a little window. We use visibility: hidden rather
-   * than display: none so layout stays stable and the urlbar floats
-   * cleanly over its slot.
-   */
-  #navigator-toolbox,
-  #zen-sidebar-splitter {
-    visibility: collapse !important;
+
+  #urlbar {
+    width: 100%;
   }
 
   &[zen-has-empty-tab="true"] {
@@ -48,9 +42,5 @@
         -moz-window-dragging: no-drag;
       }
     }
-
-    #zen-sidebar-top-buttons {
-      visibility: collapse;
-    }
   }
 }