Update _sidebar.scss

Author: vanruesc

manual/assets/css/src/screen/default/layout/_sidebar.scss

@@ -33,7 +33,7 @@
 	position: absolute;
 	transition: opacity durations.$short;
 	width: 32px;
-	z-index: layers.$hud;
+	z-index: layers.$sidebar;
 	&:focus,
 	&:hover {
 		opacity: 1;