Add active class styling for outliner items

src/app/app.css

@@ -497,6 +497,10 @@ button:disabled {
   border-color: rgba(207, 123, 66, 0.55);
 }
 
+.outliner-item--active {
+  box-shadow: inset 0 0 0 1px rgba(243, 190, 143, 0.75);
+}
+
 .outliner-item--disabled {
   border-style: dashed;
 }