UI: Tweak tab text and icon colors (#6760)

This adds a hover highlight and fades out the icon on inactive tabs.

public/less/_base.less

@@ -760,3 +760,14 @@ footer {
 .oauth2-authorize-application-box {
     margin-top: 3em !important;
 }
+
+/* Tab color tweaks */
+.ui.tabular.menu .item {
+  color: rgba(0,0,0,.5);
+}
+.ui.tabular.menu .item:hover {
+  color: rgba(0,0,0,.8);
+}
+.ui.tabular.menu .item.active {
+  color: rgba(0,0,0,.9);
+}