What can be done and what's actually done are two very different things. Fully replicating something as simple as a button can be very hard. Its look depends on

What can be done and what's actually done are two very different things. Fully replicating something as simple as a button can be very hard. Its look depends on the OS, OS version, OS theme, OS scaling setting, OS font settings, the language (left-to-right, right-to-left). It has to support all kinds of OS accessibility hooks. It has to support all kinds of input devices. It has to follow the tab-focus rules. These are just the things I'm aware without looking them up, I'm sure there's a lot more.