Total Commander

Currently (in TC 9.0b4) these margins are too thick, vertical buttonbar's width is almost twice more than buttons width... I think 2 pixels would be completely enough for margins (so it would be better to reduce left margin instead of increasing right one).

Sorry but it is necessary to have at least 3 pixels for the splitter bar.

If you configure the vertical button bar,you can keep the "small" icon size but make the buttons smaller, e.g. 20x20.