:host()
The :host()
CSS pseudo-class function selects the shadow host of the shadow DOM containing the CSS it is used inside (so you can select a custom element from inside its shadow DOM) — but only if the selector given as the function's parameter matches the shadow host. :host()
has no effect when used outside a shadow DOM.
The most obvious use of this is to put a class name only on certain custom element instances, and then include the relevant class selector as the function argument. You can't use this with a descendant selector expression to select only instances of the custom element that are inside a particular ancestor. That's the job of :host-context()
.
Note: While other functional pseudo-classes such as :is()
and :not()
accept a list of selectors as their parameters, :host()
takes a single compound selector as its parameter. In addition, while :is()
and :not()
only take into account the specificity of their argument, the specificity of :host()
is both the specificity of the pseudo-class and the specificity of its argument.
Try it
/* Selects a shadow root host, only if it is
matched by the selector argument */
:host(.special-custom-element) {
font-weight: bold;
}
Syntax
:host(<compound-selector>) {
/* ... */
}
Examples
Selectively styling shadow hosts
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:
const style = document.createElement("style");
const span = document.createElement("span");
span.textContent = this.textContent;
const shadowRoot = this.attachShadow({ mode: "open" });
shadowRoot.appendChild(style);
shadowRoot.appendChild(span);
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(.footer) { color : red; }
rule styles all instances of the <context-span>
element (the shadow host in this instance) in the document that have the footer
class set on them — we've used it to give instances of the element inside the <footer>
a special color.
Specifications
Specification |
---|
CSS Scoping Module Level 1 # host-selector |
Browser compatibility
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