Fix color of tertiary button on dark theme (#22739) (#22744)

Fix color of tertiary button on dark theme (#22739) (#22744)

Backport #22739

Before:
<img width="266" alt="Screenshot 2023-02-03 at 14 07 34"
src="https://user-images.githubusercontent.com/115237/216611151-92e98305-c4b5-42f3-b2e2-8b1b805fa644.png">

After:
<img width="271" alt="Screenshot 2023-02-03 at 14 07 52"
src="https://user-images.githubusercontent.com/115237/216611156-878a8a75-39a1-415b-9b6d-4f035985444e.png">

This is the only instance of such a button in all templates.

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>