What problem does this address?

If a user creates a custom style and then switches to another style variation, the previous customizations are lost.

In the below video, I switch the background color to a gradient. However, if I then try out different style variations, my previous settings are lost with no warning.

What is your proposed solution?

If I've made changes to my style settings, I'd expect a warning before switching to another variation letting me know that I'll lose my changes if I don't save the page first.

This might be related to saving style variations (#38333)