Dark theme: fix background for active selector items

In dropdown selectors, the background of .active items was set to the
default white background and wasn't overriden by the dark theme. This
change fixes this.

Also, the background color for focused/active items in dropdown
selectors has been changed so it contrasts more with the black
background.

Change-Id: I20d9c9092a8e03fbc0f104a038fea701c90245a4
diff --git a/src/injections/ccdarktheme.css b/src/injections/ccdarktheme.css
index 58c5689..9d9c444 100644
--- a/src/injections/ccdarktheme.css
+++ b/src/injections/ccdarktheme.css
@@ -8,7 +8,8 @@
   --TWPT-card-border: #5f6368;
   --TWPT-subtle-border: #383735;
   --TWPT-link: #8ab4f8;
-  --TWPT-thread-read-background: rgba(255, 255, 255, .08);
+  --TWPT-highlighted-item-background: rgba(255, 255, 255, .08);
+  --TWPT-thread-read-background: var(--TWPT-highlighted-item-background);
   --TWPT-drawer-background: #2d2e30;
   --TWPT-button-background: #3c3e42;
   --TWPT-green-A400: #00E676;
@@ -98,11 +99,12 @@
     material-list material-select-dropdown-item:not(.multiselect).selected,
     .popup .item-group-list material-select-item:hover,
     .popup .item-group-list material-select-item:focus,
+    .popup .item-group-list material-select-item.active,
     .popup .item-group-list material-select-dropdown-item:hover,
     .popup .item-group-list material-select-dropdown-item:focus,
     .popup .item-group-list material-select-dropdown-item.active,
     .popup .item-group-list material-select-dropdown-item:not(.multiselect).selected {
-  background-color: rgba(255, 255, 255, .04)!important;
+  background-color: var(--TWPT-highlighted-item-background)!important;
 }
 
 material-list .menu-item-label,