Merge branch 'dz-improve-sidebar-design' into 'master'

Remove background color differentiation from gitlab logo/text in sidebar
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

cc @annabeldunstone @skyruler 

See merge request !4139

app/assets/stylesheets/framework/gitlab-theme.scss

@@ -9,9 +9,6 @@
 @mixin gitlab-theme($color-light, $color, $color-darker, $color-dark) {
   .page-with-sidebar {
     .header-logo {
-      background-color: $color;
-      border-color: $color;
-
       a {
         color: $color-light;
 
@@ -21,7 +18,7 @@
       }
 
       &:hover {
-        background-color: $color-darker;
+        background-color: $color-dark;
         a {
           color: #fff;