fix(frontend): Improve low constrast of code blocks and links

[tomasr8]

Closes #2446

I changed the code block color for the closest darker green that surpasses 4.5 - Firefox is now reporting it as 4.57.

I didn't want to change the link color for all links, so I just added a new rule to target links in tables only. Firefox now reports the new value as 4.56.

Let me know if it's ok like this!

[hugovk]

I only checked the green so far, looks better.

Before:

After:

You know, I might be tempted to drop that rounded grey background box altogether, we don't have that sort of thing at https://docs.python.org/3/whatsnew/3.12.html, or keep the grey background but drop the shadow and rounder border radius.

(Possibly also ditching the green?)

[tomasr8]

Could also decrease the padding.. It looks pretty big

[JacobCoffee]

I think I like this the best out of the options:

but the current "After:" state is good, too.

[JacobCoffee]

thanks for your first contribution, @tomasr8 :)