UI refinement

Former-commit-id: 7222a5ec77fd2a961d7f6cf5593db86721677f16

src/src/main.less

@@ -680,6 +680,7 @@
 
             .append-group-list {
                 .common-popup-main-background();
+                background: rgba(30, 30, 30, .5);
                 display: none;
                 position: absolute;
                 top: 0;
@@ -718,6 +719,7 @@
                 z-index: 1001;
                 .common-colourful-background();
                 .common-popup-main-background();
+                opacity: .9;
                 padding: 10px;
                 color: #1d1d1d;