RWD(Beta) step 41 - stuck

Can you help me here? I don’t know what I do wrong there…

:not(:last-of-fieldset) {
  border-bottom: 3px solid #3b3b4f;
}

Link to challenge:

I got it.

fieldset:not(:last-of-type) {
  border-bottom: 3px solid #3b3b4f;
}