Dark theme: fix menu items styles

There was a missing comma in the CSS styles for menu items, which caused
menu items to be shown in black text over a dark background.

This change fixes this and simplifies the CSS selectors to avoid future

Fixed: twpowertools:38
Change-Id: I58bcfa143e9f77dee666b1a690deed96f776908a
diff --git a/src/static/css/ccdarktheme.css b/src/static/css/ccdarktheme.css
index 633dcaa..1ee5e11 100644
--- a/src/static/css/ccdarktheme.css
+++ b/src/static/css/ccdarktheme.css
@@ -143,10 +143,10 @@
     material-list .menu-item-label,
     material-list .label,
     material-list .text-segment,
-    .popup .item-group-list .single-select-item
-    .popup .item-group-list .menu-item-label,
-    .popup .item-group-list .label,
-    .popup .item-group-list .text-segment {
+    menu-item-groups .single-select-item,
+    menu-item-groups .menu-item-label,
+    menu-item-groups .label,
+    menu-item-groups .text-segment {
   color: rgba(255, 255, 255, .87)!important;