a11y: add keyboard operability to interface elements

[shkeating]

Suggested Changes

this branch edits the source code to make all elements keyboard operable. The original implementation used ul and li elements to show the interactive items, which prevented keybaord users from accessing them.

• All uls were changed to divs and all lis are now buttons to get them to work as expected.
• This branch also adds a clearly visible focus ring with a css variable users can adjust the color if using a css variable at the top of the stylesheet.
• some color contrast issues were remediated in the default theme as well.
• tab order issues caused by usage of absolute positioning were remediated as well

[shkeating]

oop I actually meant to only put this on my fork, but hi! I can edit this to just be the keyboard access changes and not the readme stuff if you are interested

[ksadov]

No worries! The keyboard accessibility stuff looks great, I'd love to merge that in. As far as the README goes I'd like to keep the Neocities example for this repo, but I do appreciate the Markdown correction for ./serve.sh ^_^