How to change the selected navigation color on both sides ?

[TRaSH-]

How can i change the selected navigation color on both sides ?
Because it's in my opinion much to dark to be decent readable.

1. When selected
2. When I mouse over

Probably with editing the extra.css, but i don't really understand it that well without precise instructions.

I already looked at the _colors.scss, but i can't find anything what would cover the navigations.

Added my current extra.css

[TRaSH-]

found my issue why mine didn't look readable but the example did
typo in the mkdocs.yml