How to change the color of the scroll bar in a scrolling panel?

I don't understand why the scroll bar has a normal width and format in design mode but then almost disappears when we preview or publish.  Why is one different in appearance than the other?

I agree with many above - we seem to get a lot of "latest greatest" updates that no one asked for and practical requests like horizontal scrolling and scroll panel formatting go over 12 years (I found earlier posts) with out a useful update.