theme api 'toolbar_text' element changes color of toolbar text

[CharoSW]

This may not seem like a bug by the title but for a static theme like this having elements that change color isn't great. However, as there may be situations where someone might want a to use a theme api extension (such as another extension that can tap into that api) completely setting the color of elements would probably be useful

[lunakurame]

Currently we don't support themes other than the default one, but it actually sounds like a good idea. I think those lightweight themes can also change icon colors (a CSS variable --lwt-text-color also changes icon's fill color), so if we lock it in our theme, we might be able to finally solve that old problem with icon colors being swapped on random machines.

I'll read more about the theme API and try to implement this later, thanks.