You Want border-color: transparent, Not border: none
Great tip from Dave Rupert:
If you find yourself removing a border from an element that has a border and are tempted to use border: 0 , border: none, or outline: none, I’d urge you to stop for a moment and reconsider.
Switching to border-color: transparent
makes inputs and buttons much more visible in High Contrast Mode. Huh.