This page tests several aspects of pure CSS form validation. Try to fill in the fields wrongly.
It contains rules for the following:
input:(in)valid:not(:focus)— the not-focus serves to suppress onkeypress validation and instead use onblur validation.
label:(in)valid(doesn’t work anywhere, but why leave out labels if we’ve got forms and fieldsets?)
fieldset:(in)valid niet in Edge, Android WebKit, BB10, UC