Color scheme CSS in customizer is overridden by defaults

[ryelle]

In [48371], the color scheme colors were applied to the customizer, but they seem to be overridden by higher specificity defaults. As written, the styles also need some cleanup (the highlight color shouldn't be used as a text color in most schemes). The Preview button on small screens is missing a top border on hover.

[ryelle]

The color scheme tweaks are visible on hover/focus — for example hovering over the panel titles, or the back/close buttons, focusing the media upload button.

I think the patch matches the intent from #50547, styling the borders with the button-color (which is usually the highlight-color, but in the light blue scheme it's a yellow accent), and uses the link color for the text so it stays readable on the white background.

[audrasjb]

Hi,

I forced the patch to test it. It looks good to me, but we'll have to refresh it against trunk. @ryelle if you still have the branch locally, would you mind updating your patch? Otherwise, I should be able to refresh it manually :)

[ryelle]

Thanks for testing, I've refreshed the patch.

[peterwilsoncc]

Tested the Customizer with various schemes and this does what it says on the pack. I reckon it's good to go in.

[ryelle]

In 50386:

Customizer: Bring admin color schemes back into the customizer.

In #50547, the admin color schemes were added to the customizer UI, but at some point specificity changed and the colors were overridden by the defaults. This brings the color schemes back into the customizer, using the button color as a highlight, with the link color for text to keep things readable.

Follow up to [48371].
Props audrasjb, peterwilsoncc.
Fixes #52230.