Change logo image on dark/light revealjs slides

[jthomasmock]

For revealjs slides there are often times when the slide color shifts from light to dark, for sections breaks, summaries, etcs.

It would be nice to be able to identify a dark/light logo that is then used uses the same logic as the font-color choice (revealjs auto chooses light text on dark and dark on light).

[jthomasmock]

I wasn't able to get the workaround accomplished in revealjs as the logo via YAML is a bit trickier: #1647

[mcanouil]

FYI #5439 (I'll try with revealjs to replicate).

[sagikazarmark]

Incidentally, this has been working until #4031 got "fixed".

Here is the workaround I use for now to disable logos on dark backgrounds:

.reveal.has-dark-background .slide-logo {
  display: none !important;
}

I could imagine a data- attribute that specifically allows disabling the logo on certain slides.

In addition, it would also be nice if the logo followed the background transition settings. Right now, it just appears/disappears (when the above hack is used).

[mcanouil]

See #5439 (comment) for code.
It will work as long as you have a "-light" and a "-dark" version of the images.

dark-light-revealjs.mov