Docs: Themes not working; Charts have low contrast in dark mode

[vfonic]

This is clearly not "yellow" as the browser navbar suggests.

I've only managed to get Default and Red to work.

Also, charts are impossible to read in dark mode because most of the bars/lines are black on black background.

[meleu]

I confirm this buggy behavior in the themes page.

Steps to reproduce:

• pick any theme other than default and you'll see it always look like the Red
• alternate between light and dark mode and you'll see the charts are not visible when in dark mode.

[bibstha]

Same, only shows red.