[KwanEsq]

You'd need [required] instead of [minlength] for :valid to work. The other option is :placeholder-shown, to style no-input normally, but it's newer and not as supported.

[vilmosi]

I wonder if the good old input[value=""] would work. Probably not if you have jQuery.

[bzbarsky]

No, because that matches on the HTML attribute (aka the defaultValue property in JS), not on the current value of the input.