In Mendix Marketplace you can find many widgets for customizing dropdown as per your requirement. You can click on the cart icon in your moduler and search dorpdown.
Kindly search on marketplace for dropdown widgets.
There are few more.
Check the ones which are more relevant to your requirement and see the support for the widget.
Usually Mendix provided ones have good support with newer versions. For community supported ones, check if developer community have enough support for the widget.
I feel if you have a custom requirement on a Widget area and since you know already HTML CSS and JS, you can go ahead and implement a Custom Widget or a Pluggable Widget.
The marketplace and the community can benefit from it :)