Use :focus-visible to improve focus style

[webzhao]

From :focus-visible MDN docs:

The :focus-visible pseudo-class applies while an element matches the :focus pseudo-class and the UA determines via heuristics that the focus should be made evident on the element. (Many browsers show a “focus ring” by default in this case.)

See also:

1. Keyboard-Only Focus Styles
2. :focus-visible and backwards compatibility

[AngusFu]

https://www.npmjs.com/package/postcss-focus-within