fix(ui): fix podGroup expansion background (argoproj#22279)

Signed-off-by: linghaoSu <[email protected]>

Author: linghaoSu

ui/src/app/applications/components/application-resource-tree/application-resource-tree.scss

@@ -139,6 +139,9 @@
             box-shadow: 1px 1px 1px $argo-color-gray-4;
             background-color: white;
             margin-left: 215px;
+            @include themify($themes) {
+                background-color: themed('background-2');
+            }
 
             .theme-dark & {
                 box-shadow: 1px 1px 1px $argo-color-gray-7;