Refactor zen-compact-mode.css and zen-theme.css for improved UI layout

src/browser/base/content/zen-styles/zen-sidebar.css

@@ -224,7 +224,7 @@
 
 :root:not([inDOMFullscreen='true']) #zen-sidebar-splitter {
   display: block;
-  width: 1px;
+  width: var(--zen-tabbrowser-padding);
   opacity: 0;
 }
 

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

@@ -38,7 +38,6 @@
   }
 
   #navigator-toolbox {
-    --zen-tabbrowser-padding: 5px;
     margin-top: 0; /* Issue #156 */
     order: 0 !important;
   }
@@ -436,12 +435,6 @@
     }
   }
 
-  @media not (-moz-bool-pref: 'zen.view.sidebar-expanded') {
-    #navigator-toolbox {
-      width: fit-content !important;
-    }
-  }
-
   #navigator-toolbox[zen-user-hover='true'] {
     width: fit-content !important;
   }
@@ -459,10 +452,6 @@
       padding-right: 0 !important;
     }
 
-    :root:not([zen-sidebar-legacy='true']) {
-      padding: calc(var(--zen-tabbrowser-padding) * 1.5);
-    }
-
     #zen-sidebar-splitter {
       order: 7 !important;
     }
@@ -471,6 +460,20 @@
       margin-left: 0 !important;
       margin-right: 2px !important;
     }
+
+    #tabbrowser-tabs {
+      padding-right: var(--zen-tabbrowser-padding);
+    }
+  }
+
+  @media not (-moz-bool-pref: 'zen.view.sidebar-expanded') {
+    #navigator-toolbox {
+      width: fit-content !important;
+    }
+
+    #tabbrowser-tabs {
+      padding-right: 0 !important;
+    }
   }
 
   @media (-moz-bool-pref: 'zen.view.sidebar-expanded.on-hover') and (not (-moz-bool-pref: 'zen.view.compact')) {

src/browser/base/content/zen-styles/zen-theme.css

@@ -74,6 +74,8 @@
   --zen-button-border-radius: 7px;
   --zen-button-padding: 0.6rem 1.2rem;
 
+  --zen-tabbrowser-padding: 5px;
+
   /* Other colors */
   --urlbar-box-bgcolor: var(--zen-urlbar-background) !important;
   --toolbar-field-focus-background-color: var(--urlbar-box-bgcolor) !important;