Fix inconsistent background color for filter input field

CHANGELOG

@@ -12,6 +12,7 @@ v 8.12.0 (unreleased)
   - Optimistic locking for Issues and Merge Requests (title and description overriding prevention)
   - Add `wiki_page_events` to project hook APIs (Ben Boeckel)
   - Remove Gitorious import
+  - Fix inconsistent background color for filter input field (ClemMakesApps)
   - Add Sentry logging to API calls
   - Automatically expand hidden discussions when accessed by a permalink !5585 (Mike Greiling)
   - Fix groups sort dropdown alignment (ClemMakesApps)

app/assets/stylesheets/framework/nav.scss

@@ -211,12 +211,6 @@
       }
     }
 
-    .project-filter-form {
-      input {
-        background-color: $background-color;
-      }
-    }
-
     @media (max-width: $screen-xs-max) {
       padding-bottom: 0;
       width: 100%;