background color of the tab bar should be light gray for "Sidebar" style with auto-hide.

skin/classic/treestyletab/sidebar/base.css

@@ -14,6 +14,11 @@
 	background: transparent !important;
 	background-color: #d4dde5 !important;
 }
+/* autohide */
+.treestyletab-tabbar-toolbar[treestyletab-tabbar-autohide][treestyletab-mode="vertical"]
+  #treestyletab-tabbar-resizer-box {
+	background: rgba(212, 221, 229, 0.75);
+}
 
 /* Don't display unnecessary clutter */
 .tabbrowser-tabs[treestyletab-mode="vertical"]
@@ -404,6 +409,7 @@ tabbrowser[treestyletab-mode="vertical"]
 	border: 0 none !important;
 }
 
+
 /* for Multiple Tab Handler */
 .tabbrowser-tabs[treestyletab-mode="vertical"]
   .tabbrowser-tab:not(:hover):not([selected="true"])[multipletab-ready-to-close="true"]

skin/classic/treestyletab/sidebar/inactive-3.6.css

@@ -13,6 +13,12 @@
   .tabbrowser-strip:not([treestyletab-style~="aero"])[treestyletab-mode="vertical"] {
 	background-color: #e8e8e8 !important;
 }
+/* autohide */
+#main-window:not([active="true"])
+  .treestyletab-tabbar-toolbar[treestyletab-tabbar-autohide]:not([treestyletab-style~="aero"])[treestyletab-mode="vertical"]
+  #treestyletab-tabbar-resizer-box {
+	background: rgba(232, 232, 232, 0.75);
+}
 
 /* Use the splitter to display the border of .tabbrowser-strip */
 #main-window:not([active="true"])

skin/classic/treestyletab/sidebar/inactive-4.css

@@ -15,6 +15,12 @@
   .tabbrowser-strip:not([treestyletab-style~="aero"])[treestyletab-mode="vertical"] {
 	background-color: #e8e8e8 !important;
 }
+/* autohide */
+#main-window:-moz-window-inactive
+  .treestyletab-tabbar-toolbar[treestyletab-tabbar-autohide]:not([treestyletab-style~="aero"])[treestyletab-mode="vertical"]
+  #treestyletab-tabbar-resizer-box {
+	background: rgba(232, 232, 232, 0.75);
+}
 
 /* Use the splitter to display the border of .tabbrowser-strip */
 #main-window:-moz-window-inactive