Change the dark-mode hyperlink colour for a higher contrast ratio and make all hyperlink underlines more visible

[samcunliffe]

See parent issue for more explaination. But the releavent part of James' email:

As there are quite a lot of hyperlinks on all pages, it would be great if their dark-mode colour could be lightened until they have a contrast ratio of 4.5:1 or more against both the background colour (#27262b; current ratio is 4.13:1) and the slightly lighter code text background (#31343f; current ratio is 3.41:1); a contrast checker can be used to find the best colour options. Increasing the visibility of the links' underline would also really help, to provide an additional visual means to know that a link is a link, as it's currently nearly invisible in both modes.

Definition of done

Dark mode link colour contrasts more with the background.
Hyperlink underline style is thicker.

Ideas dump

PR to upstream theme? Hack the theme ourselves? Change theme completely (but then we risk breaking more than we fix)

[samcunliffe]

Looks like

• Improve color contrast for default colors and UI elements just-the-docs/just-the-docs#1258

might be related.

[cuteshaun]

Thanks for the detailed breakdown! I’ve picked this up