Before this post check: When simple overriding is not possible!
In this post I will show why would you have to change the flex classes code.
I had hard times with this problem. When both scrollers appear in a container in the same time, a white rectangle is created in the corner. First I thought it’s something with the scroller (that’t why I didn’t find the solution). But I’ve found it! And I have to ask a question: Why is that the the rectangle have to be white, and it is hardcoded there?