Is it possible to set the CSS or control the style of the "active" button in a navigation menu?
What you can do via the editor is the only thing you can do. you can't control it via Corvid.
But you can build a custom menu of your own from scratch and have full control over it.
You can't edit the css in Wix, you can only use Wix Editor own settings to design your menu.
If you want more control then make up your own menu.
As J .D. already says above lol