Update site colors somewhat

[BenDMyers]

This pull request has a few style updates, namely:

• Make upcoming events' View Details links gold, to lean into the gold theme.

• Customize events' View Details links' focus outlines using :focus-visible. Now, when a keyboard user tabs to any of the View Details links, their focus outline will be dark gold, and will have more padding.

• Shrink View Details links a bit when they're being pressed (:active), to give a slightly more tactile, three-dimensional effect

• Changed site background to a very, very light gray. This has the effect of making the white event cards and any white backgrounds in our embeds stand out more.

[chantastic]

love it! thank you 🙏

[BenDMyers]

@chantastic Aren't you out today? 😛

[chantastic]

potty break. couldn't help checking in on my favorite repo 😁