Or just default Light and Dark modes?

How do Light/Dark modes work in conjunction with color themes?

via CSS

Light and dark are the only two options. If you want different coloured theme variations (some football sites do this for each team), you can create multiple themes, or you can try implementing your own color picker using JS and CSS.

1 hour ago, Ehren said:

Light and dark are the only two options. If you want different coloured theme variations (some football sites do this for each team), you can create multiple themes, or you can try implementing your own color picker using JS and CSS.

So the themes created in v4 would still be available in v5 using custom.css?

No, the entire CSS framework has changed - so you’ll need to redo most of your custom CSS for v5.