Solves#46 (with rather a lot of code).

Summary

Introduce a dependency ontinycss2. Thenuse it via some ...err... "convenience" parsing functions. Hopefully, these are clear and somewhat reusable for our eventual solution of#86.

Testing

Added a unit test for my function. Open to adding test cases if anyone can think of anything.

Reviewer notes:

The other ways to solve#46 is via a regex (~5 LoC) or viathing.setIconSize(QSize(28, 28)) (2 LoC). Compare those with this @ ~30 LoC. 🙃

Argument for doing it this way

Boils down to#86. We should be able to parse other colours from the "current" CSS file with these functions. Then do an internal update of the axes colours etc (currently most of the code inNapariMPLWidget.apply_napari_colorscheme). And Ithink our update code could be connected toviewer.events.theme (undocumented... we can probably test quite easily and fix the docs upstream either way).

Against

I'm actually increasingly open to a regex solution.It's what napari themselves seem to do. Opinions gratefully received.

Could also reuse the tdd and do the regex infrom_css_get_the_size_of.

Also if anyone knows of a better way to customise my subclass's constructor whilst keeping the type checker happy. Like maybe there's a better design decision to be made somewhere? Discussion of interest...

• Method signature forwarding for subclasses python/typing#1079