When i was a little kid, I was really scared of the dark. But then I came to understand, dark just means the absence of photons in the visible wavelength -- 400 to 700 nanometers. Then i thought, well, its really silly to be afraid of a lack of photons. Then i wasn't afraid of the dark anymore after that.
Elon Musk

:valid

The :valid CSS pseudo-class represents any <input> or other <form> element whose contents validate successfully. This allows to easily make valid fields adopt an appearance that helps the user confirm that their data is formatted properly.
:valid css reference