lib: Give secondary buttons more contrast in toolbars

[mvollmer]

Secondary buttons have a transparent background by default, which needs more contrast on grey backgrounds like in toolbars.

[martinpitt]

Technical review 👍 . Happy to give a formal ack if you already agreed on this with Garrett someplace else. Thanks!

[martinpitt]

@mvollmer would you mind putting a before/after screenshot? that may make it easier for @garrett to review.

[garrett]

I agree with this sentiment and the CSS looks like what I'd suspect. I'd be able to approve it with a screenshot. 😉

[garrett]

Also: Note: This would affect all buttons, regardless of context (what other widgets they're in), so it might have some unknown effects in some places.

It's probably correct, however.

[mvollmer]

The hostswitcher has changed in light mode:

as opposed to earlier:

This does increase the contrast, and now the buttons have the same background color as the text input box. So I guess it's correct in that sense and looks as intended.

[mvollmer]

The rest of the pixel changes are as expected. For example, the secondary buttons on the Networking page now look like this in dark mode:

as opposed to: