Fail enough. I went and tried the answer without quick luck. After some trial and error, in the simplest working page:

This gets you a status bar with black background and white text:

    <p>Testing Status bar: white text text, black background</p>

This gets you a status bar with white background and black text:

    <p>Testing Status bar: black text, white background</p>

the important detail is getting the theme inside the body element not the head. Other colors can be used too, for example, a red status bar:

I don’t really have time to apply this in the voyager app and I don’t use it either, so I’m not really motivated to do it atm. Just for the sake of it, I’ve downloaded the code and tried to apply the changes I though it would make it work, but it was not a straight forward fix, so I gave up.