Fix white components backgrounds when OS is using dark theme

[LukasMasuch]

Describe your changes

I previously attempted to fix this issue in #7821. This fix worked fine, but only if the OS isn't configured to dark mode (+ Chrome). This fix sets the color scheme to normal to indicate that the element isn't aware of any color schemes. This seems to provide us with the desired behaviour to not automatically show a white background.

GitHub Issue Link (if applicable)

Closes #8156
Closes #7813

Testing Plan

• The test should be fine to cover this.

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[kmcgrady]

Making sure I understand, we are effectively unsetting the color scheme (cause normal is the default and color-scheme is inherited).

Does this seem more helpful to just say that all iframes have color-scheme: normal in the global styles? Just avoids the need to remember this for the next time?

[LukasMasuch]

Making sure I understand, we are effectively unsetting the color scheme (cause normal is the default and color-scheme is inherited).

Yep, exactly 👍

Does this seem more helpful to just say that all iframes have color-scheme: normal in the global styles? Just avoids the need to remember this for the next time?

yeah, might make sense but I need to think a bit more about that. There could be some potential unexpected side-effects if we just apply this to all iframes. Another way to improve this might be to share a customized Iframe component between multiple elements. There are other properties that might make sense to have shared across multiple iframe uses.