feat(video rooms): highlight participants icon

Previously, when other users had joined a video room, the difference displayed to the local user was very subtle. Now, the participants icon will always display as a colour, to draw the users attention.

Author: hazzuk

res/css/views/rooms/_LiveContentSummary.pcss

@@ -34,11 +34,17 @@ Please see LICENSE files in the repository root for full details.
         }
     }
 
+    /* elecord, highlight participants */
+    .mx_LiveContentSummary_participants {
+        color: var(--cpd-color-text-action-accent);
+    }
+
     .mx_LiveContentSummary_participants::before {
         display: inline-block;
         vertical-align: text-bottom;
         content: "";
-        background-color: $secondary-content;
+        /* background-color: $secondary-content; */
+        background-color: var(--cpd-color-text-action-accent);
         mask-image: url("$(res)/img/element-icons/group-members.svg");
         mask-size: 16px;
         width: 16px;