I used to work for High 5 Games, a developer of slot games content. I was responsible for all the artwork except for the painted portraits of the character's faces. I created all the frames, logos, symbols, background art, and any other UI elements seen below.
Some years ago, a gaming community website asked me to create web skins for them. I was asked to use the artwork and logos from fan kits and/or the game's official website. And, with a couple of exceptions here and there, I had to build the actual frames, buttons, hover states, and clicked states from scratch, matching the existing aesthetic and page format.
The below are just a few UI tidbits from random projects. Some are incomplete due to the projects being cancelled.