Way back in #187, I introduced a hacky tool to show the available space
on a slide: it was a `mdbook` plugin which injected the necessary CSS on
each slide. Crude, but it got the job done.
The logic was moved from Python to a real CSS file with associated
JavaScript in #1842. In #1917, the functionality was moved to a
dedicated “instructor menu”, together with functionality for saving the
state of the Playground on each slide.
Unfortunately, the whole thing was disabled in #1935 since I found that
the Playgrounds lost their code with the saving logic. I was also not
100% happy with dedicating space on each slide for a menu only used by
instructors.
However, I really think we need a tool to let slide editors know about
the available space, so I would like to re-introduce the red box. This
time via a keyboard shortcut to make it easy to toggle as needed.
I’m suggesting enabling this for everyone, with the expectation that
most people won’t find the shortcut and will quickly disable the box if
they do (there is a dedicated button to hide it again).
End-to-end tests have been added for the new functionality.
The embedded Playground's code reset when you navigate between slides.
This has caused problems: if people navigate away from a slide to look
something up, they've suddenly lost their work.
Added a dev theme to help with slide aspect ratio while updating content
or for reviewing PRs.
Fixes#1796.
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Co-authored-by: Dustin J. Mitchell <djmitche@google.com>
Co-authored-by: Martin Geisler <martin@geisler.net>
