ta-link-type="dfn" href="https://drafts.csswg.org/selectors-4/#pseudo-class" id="ref-for-pseudo-class①">pseudo-class</a> to select elements with specific states.
The former is the <code class="idl"><a data-link-type="idl" href="#dom-elementinternals-states" id="ref-for-dom-elementinternals-states">states</a></code> IDL attribute of
<code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/custom-elements.html#elementinternals" id="ref-for-elementinternals">ElementInternals</a>