This is a simple change you can immediately notice. I hope this looks better.
Also I found that scrollbar customization is working on OBS 27.0.1 Browser, so I changed the look of it. Finally all the three rounded corners are now visible. I made the top-left corner to be not round so users can use the corner pixel to tell if cropping worked well. But I don't know if anyone is actually doing that, so I might make it round later.
Background returned to black. As I changed the control panel to be dark, it would be stressing eyes if the default background is still white (fallback from transparent).