I’m working on a couple of reveal.js themes for dev rel. They are not in their own repo yet but in my presentation deck. Look at the template folder for a demo.
The themes are mozilla-devrel-light.css and mozilla-devrel-dark.css. The reveal.js lib there has a modification in the highlight component allowing data-dim property for dimming not highlighted source code.
These themes include no branding images (but the template presentation does) and just a rule for setting tabzilla color if included. Install tabzilla if you want our famous tab.