Why do styles disappear in Google chrome when scrolling inside a position: fixed element?

Question

css

Sample code here
There is a position: fixed container, it has a scrollbar, there are elements inside it and they can be scrolled.
One of these elements has class="selected" written on it. This class sets the background. If you scroll down and then back to the selected class="selected" element, the background disappears.
WTF? How to overcome it?

Answer 1

You need to set the child elements to position: relative; then everything will be fine

Answer 2

nothing is lost. Look through the console. Most likely there is some script that removes the selected class

Answer 3

Perhaps I encountered something similar when opening the lists. Just put between scroll blocks
<div style="clear: both; "></div>