Remove navbar gradient

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

@@ -6,7 +6,7 @@
   // Header
 
   header.navbar-gitlab-new {
-    background: linear-gradient(to right, $color-900, $color-800);
+    background-color: $color-900;
 
     .navbar-collapse {
       color: $color-200;
@@ -201,7 +201,7 @@ body {
     @include gitlab-theme($theme-gray-900, $theme-gray-700, $theme-gray-800, $theme-gray-700, $theme-gray-700, $theme-gray-100, $theme-gray-700);
 
     header.navbar-gitlab-new {
-      background: $theme-gray-100;
+      background-color: $theme-gray-100;
       box-shadow: 0 2px 0 0 $border-color;
 
       .logo-text svg {