Global styles: custom styles don't persist after style switching

[junglej77]

Description

When switching global styles, the custom styles (e.g., font size set to XXL) are not persisting. After switching to another global style (e.g., Style A) and back to the default style, the previous custom changes are lost.

Steps to Reproduce

1. Go to the Global Styles panel.
2. Modify the font size (e.g., set it to XXL).
3. Switch to a different global style (e.g., Style A).
4. Switch back to the default global style.
5. The font size change is lost, and the global style reverts to the original default settings.

Expected Behavior

I expect the custom styles to persist after switching between global styles. For example, when I modify the font size in the default global style, switch to Style A, and then return to the default style, I expect the custom font size to remain as XXL.

Additional Context

Gutenberg version: [Include the version you're using]
WordPress version: [Include your WordPress version]

[annezazu]

Thanks for opening this issue! Previously, this feedback has been stored here: #46397 (comment)

Can we close this out in favor of that issue, unless I'm missing something?