Update dos/donts in dark mode

[katjuell]

Description

Resolves #633 by updating colors for dos/donts in dark mode.

Test process

Go through the register/profile show flow and check that dark mode styles look reasonable.

Requirements to merge

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code in hard-to-understand areas
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes