UX: Site setting filter background inconsistencies (#30393)

Followup 203f93bcaf

This commit makes sure the background for all the admin
site settings filters (including the filter input and
override checkbox) is consistent no matter what the theme,
as it currently changes based on theme.

app/assets/stylesheets/common/admin/admin_config_area.scss

@@ -92,17 +92,22 @@
   }
 
   &__settings {
-    .admin-site-settings-filter-controls {
-      background: var(--primary-very-low);
-      margin-bottom: 1em;
-    }
-
     .setting-label {
       margin-left: 18px;
     }
   }
 }
 
+.admin-site-settings-filter-controls {
+  background: var(--primary-very-low);
+  margin-bottom: 1em;
+
+  .controls,
+  .search.controls {
+    background: var(--primary-very-low);
+  }
+}
+
 .admin-config-area-empty-list {
   padding: 1em;
   border: 1px solid var(--primary-low);

app/assets/stylesheets/common/admin/site-settings.scss

@@ -10,11 +10,6 @@
 
 .admin-plugin-config-area {
   &__settings {
-    .admin-site-settings-filter-controls {
-      background: var(--primary-very-low);
-      margin-bottom: 1em;
-    }
-
     .admin-filtered-site-settings {
       padding: 0.5em 1em;
     }

config/locales/client.en.yml

@@ -5108,7 +5108,7 @@ en:
   # This section is exported to the javascript for i18n in the admin section
   admin_js:
     # This is a text input placeholder, keep the translation short
-    type_to_filter: "type to filter…"
+    type_to_filter: "Type to filter…"
     settings: "Settings"
 
     admin: