* Fix all stylelint errors
For any errors that fixing would require changing the output of the css disable stylelint for that line instead of modifying.
* Update quality.py
Make stylelint quality check pass when there are no errors
* Delete empty selectors
In the dashboard header and the course navigation bar, the current
tab is supposed to be the only one with a bottom border. But in
high contrast mode in Windows, all of them were assigned a bottom
border color.
So instead of toggling the color when active, toggle the border
style, since Windows overrides our color choice anyway.
LEARNER-3219
