[qualiteam]

I would decorate the TopCategories class and make it display the drop-down list instead of the regular one.

Actually, it can render the drop-down menu already, but is missing necessary CSS files.

So, what you need to make it drop down:

1. Decorate the TopCategories class in your module.

2. In the defineWindgetParams() methods, after executing the parent one, change the value of the static::PARAM_DISPLAY_MODE widget parameter to static:: DISPLAY_MODE_TREE.

3. Add necessary styles through the getCSSFiles() method.