Set correct icon in courseware block adder list

CoursewareExcalidrawBlockPlugin.php

@@ -22,7 +22,7 @@ class CoursewareExcalidrawBlockPlugin extends StudIPPlugin implements \SystemPlu
         // Add CSS to set the correct icon for the block in the block adder
         $icon = Icon::create('block-canvas');
         \PageLayout::addStyle(
-            '.cw-blockadder-item.cw-blockadder-item-excalidraw {
+            '.cw-blockadder-item-list .cw-blockadder-item.cw-blockadder-item-excalidraw {
             background-image:url(' . $icon->asImagePath() . ')
         }'
         );