::part()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2020.

::part は CSS の擬似要素で、一致する part 属性を持つシャドウツリー内の任意の要素を表します。

css

custom-element::part(foo) {
  /* `foo` の部分に適用するスタイル */
}

構文

css

::part(<ident>+) {
  /* ... */
}

例

HTML

html

<template id="tabbed-custom-element">
  <style>
    *,
    ::before,
    ::after {
      box-sizing: border-box;
      padding: 1rem;
    }
    :host {
      display: flex;
    }
  </style>
  <div part="tab active">Tab 1</div>
  <div part="tab">Tab 2</div>
  <div part="tab">Tab 3</div>
</template>

<tabbed-custom-element></tabbed-custom-element>

CSS

css

tabbed-custom-element::part(tab) {
  color: #0c0dcc;
  border-bottom: transparent solid 2px;
}

tabbed-custom-element::part(tab):hover {
  background-color: #0c0d19;
  color: #ffffff;
  border-color: #0c0d33;
}

tabbed-custom-element::part(tab):hover:active {
  background-color: #0c0d33;
  color: #ffffff;
}

tabbed-custom-element::part(tab):focus {
  box-shadow:
    0 0 0 1px #0a84ff inset,
    0 0 0 1px #0a84ff,
    0 0 0 4px rgb(10 132 255 / 30%);
}

tabbed-custom-element::part(active) {
  color: #0060df;
  border-color: #0a84ff !important;
}

JavaScript

let template = document.querySelector("#tabbed-custom-element");
globalThis.customElements.define(
  template.id,
  class extends HTMLElement {
    constructor() {
      super().attachShadow({ mode: "open" }).append(template.content);
    }
  },
);

結果

仕様書

Specification
CSS Shadow Parts # part

ブラウザーの互換性

BCD tables only load in the browser