Part 1 by Markkoenig : The Basics
Part 2 by slowboyfast : Composition & Graphics
Part 3 by cliffflip : Creating Panel Switchers
Part 4 by cliffflip: Avoiding truncated Panels
Part 5 by cliffflip: Elements Relative Position & Size
Reference:
jam.cliffflip.com/2017/03/how-to-skin-foobar2000-part-1