Remove focus ring when clicking on toggle buttons

[jacob314]

Unless users are trying to keyboard navigate it would be nice to not display it particularly if the user just clicked on a button and didn't try to do anything explicitly toggling focus.
For example, see:
https://hackernoon.com/removing-that-ugly-focus-ring-and-keeping-it-too-6c8727fefcd2

[kenzieschmoll]

this only applies to the dart:html app, which is now deleted