🐛 Fix popup menu background transparent bug

components/menu/style/index.less

@@ -180,6 +180,7 @@
       position: absolute;
       border-radius: @border-radius-base;
       z-index: @zindex-dropdown;
+      background: @menu-popup-bg;
 
       .submenu-title-wrapper {
         padding-right: 20px;

components/style/themes/default.less

@@ -322,6 +322,7 @@
 @menu-item-height: 40px;
 @menu-collapsed-width: 80px;
 @menu-bg: transparent;
+@menu-popup-bg: @component-background;
 @menu-item-color: @text-color;
 @menu-highlight-color: @primary-color;
 @menu-item-active-bg: @item-active-bg;