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

Great theme but the latest update turns the new tab page grey and it doesn't display properly for me