Day 70: the defined pseudo-class

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It’s time to get me up to speed with modern CSS. There’s so much new in CSS that I know too little about. To change that I’ve started #100DaysOfMoreOrLessModernCSS. Why more or less modern CSS? Because some topics will be about cutting-edge features, while other stuff has been around for quite a while already, but I just have little to no experience with it.

:defined represents any element that has been defined. This includes standard elements and custom elements that have been successfully defined.

:defined {
background-color: #000;
color: #fff;

Standard elements

<p>I'm defined</p>
<small>I'm defined</small>

I'm defined

I'm defined

Undefined custom elements

<unde-fined>I'm not defined</unde-fined>
I'm not defined

Defined custom elements

<de-fined>I'm defined</de-fined>
class BasicComponent extends HTMLElement {
constructor() {

customElements.define('de-fined', BasicComponent);
I'm defined

Deprecated elements

test test

See on CodePen.

Further reading