Steam Skins
Over the years Steam has been slowly replacing aspects of the Steam Client from VGUI to a web-based framework called Chromium Embedded Framework On April 27th, 2023 Steam skins completely lost support and only work through community based patching methods.
History
Removal of skin support for the Friends List on July 24th 2018
Removal of skin support for the Library on October 30th 2019
Removal of skin support for the main window frame and all additional windows in Steam Beta on April 27th 2023
The above update was later pushed to all users since June 15, 2023, completely removing skin support for all common windows.
Can I Still Install themes?
Yes, Steam themes still exist! And the community is still thriving!
How to install themes in 2024
As the official skin support (for VGUI) has been removed, with the new CEF-based UI not providing any official way of changing skins, it was unofficially replaced by Millennium for Steam For Windows 10+
Millennium is an open source patcher that allows skins/themes after April 27th 2023. view source
Setting Up
Refer to this page Installation Guide
Finding Themes
The main sources for up-to-date themes are found on this website