Actual steam UI skins.

[LoveAndPeace]

Would be amazing because sometime you just want your UI to match your theme.
It's gotten pretty bland and a open source project like RetroPie has tons of skin in less than a few years now.

[C²C^Guyver |NZB|]

The client had the ability to use third-party skins. That ability was removed. I doubt that it ever comes back.

Your account is old enough to remember this being a thing. It's strange that you don't remember.