The :host CSS pseudo-class selects the shadow host of the shadow DOM containing the CSS it is used inside — in other words, this allows you to select a custom element from inside its shadow DOM.

Note: This has no effect when used outside a shadow DOM.

/* Selects a shadow root host */
:host {
  font-weight: bold;




Styling the shadow host

The following snippets are taken from our host-selectors example (see it live also).

In this example we have a simple custom element — <context-span> — that you can wrap around text:

<h1>Host selectors <a href="#"><context-span>example</context-span></a></h1>

Inside the element's constructor, we create style and span elements, fill the span with the content of the custom element, and fill the style element with some CSS rules:

let style = document.createElement('style');
let span = document.createElement('span');
span.textContent = this.textContent;

const shadowRoot = this.attachShadow({mode: 'open'});

style.textContent = 'span:hover { text-decoration: underline; }' +
                    ':host-context(h1) { font-style: italic; }' +
                    ':host-context(h1):after { content: " - no links in headers!" }' +
                    ':host-context(article, aside) { color: gray; }' +
                    ':host(.footer) { color : red; }' +
                    ':host { background: rgba(0,0,0,0.1); padding: 2px 5px; }';

The :host { background: rgba(0,0,0,0.1); padding: 2px 5px; } rule styles all instances of the <context-span> element (the shadow host in this instance) in the document.


Specification Status Comment
CSS Scoping Module Level 1
The definition of ':host' in that specification.
Working Draft Initial definition.

Browser compatibility

BCD tables only load in the browser

See also