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.

Try it

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


:host {
  /* ... */


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:

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

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:

const style = document.createElement("style");
const 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: rgb(0 0 0 / 10%); padding: 2px 5px; }";

The :host { background: rgb(0 0 0 / 10%); padding: 2px 5px; } rule styles all instances of the <context-span> element (the shadow host in this instance) in the document.


CSS Scoping Module Level 1
# host-selector

Browser compatibility

BCD tables only load in the browser

See also