Change sidebar drop shadow to rgba

app/assets/stylesheets/framework/sidebar.scss

@@ -17,7 +17,7 @@
     height: 100%;
     overflow: hidden;
     transition: width $sidebar-transition-duration;
-    @include box-shadow(2px 0 16px 0 $box-shadow-gray);
+    @include box-shadow(2px 0 16px 0 $black-transparent);
   }
 }

app/assets/stylesheets/framework/variables.scss

@@ -86,7 +86,6 @@ $todo-alert-blue: #428bca;
 $btn-side-margin: 10px;
 $btn-sm-side-margin: 7px;
 $btn-xs-side-margin: 5px;
-$box-shadow-gray: #bbb;
 /*
  * Color schema