* test_tailwind: include custom stylesheet
* [REF-3004] Use relative path to stylesheet for postcss-import compat
postcss-import balls all of the CSS up into a single file, which happens at
compile time. So, replace the `@/` with `../public` so the import paths can be
resolved relative to the `styles` directory.
* test_compiler: fix compile_stylesheets expectations
* Use constants.Dirs.PUBLIC instead of "public"
* add more tests
* add tests to raise coverage
* more tests, bump coverage to 73
* fix up icon_button test
* fix darglint for app.py
* fix utcnow usage warning
* set threshold to 72
* fix timestamp
* fix unit tests for linux-redis
* removed commented code and put a TODO
* pass lang and custom_attrs from app to html root
* fix some pre-commit errors and try adding lang
* fix tests
* really fix test
* cleanup with @benedikt-bartscher
* fix props and tests
* use str instead of var
* change typing of html_custom_attrs to not allow Vars
