[Middle Click Scroll] Mouse scroll icon is not shown on top of some screen elements

[julealgon]

When scrolling through the new commit details diff panes, I noticed that the main scroll icon (the icon that appears when one presses the middle mouse button) shows properly initially, but when the mouse moves away from it, some elements in the windows are rendered on top of the icon, namely the red and green highlights on diffs.

This is obviously a minor issue but I figured I'd file it since I wasn't able to find a similar one documented.