Derive code block theme colors from code theme instead of page theme

[Brendonovich]

A user may want to use dark theme code in their site's light theme. Currently, the code will highlight correctly, but the background and tabs will stay in light mode, leading to this

[jer3m01]

We could change the selector for css variables from:
https://github.com/kobaltedev/solidbase/blob/main/src/default-theme/variables.css#L56

html[data-theme*="dark"]

to like html[data-theme*="dark"], [data-theme*="dark"] > * and that should allow parent nodes to change the local colors.
(idk if that css selector actually works, also need it for forcing light)