Validate more interactive features (completion, etc)

[nrbgt]

Users report hard-to-read text in completions. Do a pass through all the LSP/JKM features to verify contrast.

[nrbgt]

[sanbales]

Wonder if you could programmatically run through the possible combinations of foreground and background colors and make sure the contrast is >4.5.

https://stackoverflow.com/questions/9733288/how-to-programmatically-calculate-the-contrast-ratio-between-two-colors

[nrbgt]

PRs welcome!

if imma do that, it's going to be like pydata/pydata-sphinx-theme#294 and fix lab core first.