I found a way to fix the new tab background, follow this answer: https://superuser.com/a/319322 except in step 5 paste this into the file:

body { --newtab-background-color: inherit !important; }

Love the theme, exactly what I was looking for! Small hick-up though, in the last update the "new tab" page background appears dark grey / blue, which doesn't look very nice and makes the text hard to read.

It's a great theme, but with the last update the new tab does not display properly