Windows forms is based on decides old WinApi. There's some support for styling there, e.g. owner drawn items, custom painted controls, but using it correctly is

Windows forms is based on decides old WinApi. There's some support for styling there, e.g. owner drawn items, custom painted controls, but using it correctly is tricky as hell. WPF is based on Direct3D 9, and is easily stylable. I consider it is the gold standard. But it is Windows only. There are cross platform alternatives, xamarin, avalonia, but I don't have hands on experience with them.