Hover effects shouldn't decrease contrast/opacity in header

[JoshuaKGoldberg]

What version of starlight are you using?

0.34.3

What version of astro are you using?

5.9.2

What package manager are you using?

pnpm (n/a)

What operating system are you using?

Mac (n/a)

What browser are you using?

Chrome

Describe the Bug

Coming over from https://github.com/JoshuaKGoldberg/OctoGuide/pull/153/files#r2138624937 (thanks @azat-io!): hovering over header social media links and theme toggles decreases their opacity. The decrease isn't enough to make them wholly inaccessible, but:

• It's inconsistent with how the search bar increases contrast on hover:
  
• I've seen folks recently espousing that hover should increase contrast, as hovering is a way many users signal what they're reading
  • I can't find any specific articles but here's a nice Bluesky post 😅 https://bsky.app/profile/una.im/post/3lqttzwqzac2p

Suggestion: instead of lowering icon opacity on hover, how about changing their color to something slightly darker? For example, on starlight.astro.build, that might be #0f1c8a (--sl-color-accent-high) instead of #3d50f5 (--sl-color-accent)?

Link to Minimal Reproducible Example

https://stackblitz.com/github-ekc1tvww

Participation

• I am willing to submit a pull request for this issue.

[delucis]

Thanks for the suggestion @JoshuaKGoldberg!

The other option would be var(--sl-color-white) (#ffffff in dark mode, #17181c in light mode), which would mirror what links do in other parts of Starlight’s styles.

I’d be happy to receive a PR for this if you’re still up for it?

(Going to move this to our discussions in the meantime as not strictly speaking a “bug”, more of a suggested improvement.)

[JoshuaKGoldberg]

Great thanks! TBH I'm pretty swamped right now 😅 and don't think I can get time for a PR soon. But eventually hopefully maybe! If someone else sends a PR I'd happily cheer it on.