fix(plugins/plugin-client-common): sidecar top tabs may not have the proper sidecar header color

Fixes #6841

Author: starpit

plugins/plugin-client-common/web/scss/components/Sidecar/Base.scss

@@ -14,11 +14,15 @@
  * limitations under the License.
  */
 
-@import '_mixins';
+@import 'mixins';
 
 @include Sidecar {
   &,
   .kui--tab-content {
     background-color: var(--color-sidecar-background-01);
   }
 }
+
+@include SidecarTopTabs {
+  background-color: var(--color-sidecar-header);
+}

plugins/plugin-client-common/web/scss/components/Sidecar/_mixins.scss

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-@import '../Terminal/_mixins';
+@import '../Terminal/mixins';
 
 @mixin sidecar-maximized-no-user {
   .toggle-sidecar-maximization-button {