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  <span slot="heading">Hello world</span>
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<button id="launch-dialog">Launch dialog</button>
              #launch-dialog {
  background: tomato;
  border-radius: 4px;
  color: #fff;
  font-family: Helvetica, Arial, sans-serif;
  padding: 0.5rem 1rem;
  position: static;
              'use strict';

class OneDialog extends HTMLElement {
  static get observedAttributes() {
    return ['open'];
  constructor() {
    this.attachShadow({ mode: 'open' });
    this.close = this.close.bind(this);
  attributeChangedCallback(attrName, oldValue, newValue) {
    if (oldValue !== newValue) {
      this[attrName] = this.hasAttribute(attrName);
  connectedCallback() {
    const { shadowRoot } = this;
    shadowRoot.innerHTML = `<style>
      .wrapper {
        opacity: 0;
        transition: visibility 0s, opacity 0.25s ease-in;
      .wrapper:not(.open) {
        visibility: hidden;
      .wrapper.open {
        align-items: center;
        display: flex;
        justify-content: center;
        height: 100vh;
        position: fixed;
          top: 0;
          left: 0;
          right: 0;
          bottom: 0;
        opacity: 1;
        visibility: visible;
      .overlay {
        background: rgba(0, 0, 0, 0.8);
        height: 100%;
        position: fixed;
          top: 0;
          right: 0;
          bottom: 0;
          left: 0;
        width: 100%;
      .dialog {
        background: #ffffff;
        max-width: 600px;
        padding: 1rem;
        position: fixed;
      button {
        all: unset;
        cursor: pointer;
        font-size: 1.25rem;
        position: absolute;
          top: 1rem;
          right: 1rem;
      button:focus {
        border: 2px solid blue;
    <div class="wrapper">
    <div class="overlay"></div>
      <div class="dialog" role="dialog" aria-labelledby="title" aria-describedby="content">
        <button class="close" aria-label="Close">✖️</button>
        <h1 id="title"><slot name="heading"></slot></h1>
        <div id="content" class="content">
    shadowRoot.querySelector('button').addEventListener('click', this.close);
    shadowRoot.querySelector('.overlay').addEventListener('click', this.close);
    this.open = this.open;
  disconnectedCallback() {
    this.shadowRoot.querySelector('button').removeEventListener('click', this.close);
    this.shadowRoot.querySelector('.overlay').removeEventListener('click', this.close);
  get open() {
    return this.hasAttribute('open');
  set open(isOpen) {
    const { shadowRoot } = this;
    shadowRoot.querySelector('.wrapper').classList.toggle('open', isOpen);
    shadowRoot.querySelector('.wrapper').setAttribute('aria-hidden', !isOpen);
    if (isOpen) {
      this._wasFocused = document.activeElement;
      this.setAttribute('open', '');
      document.addEventListener('keydown', this._watchEscape);
    } else {
      this._wasFocused && this._wasFocused.focus && this._wasFocused.focus();
      document.removeEventListener('keydown', this._watchEscape);
  close() {
    if (this.open !== false) {
      this.open = false;
    const closeEvent = new CustomEvent('dialog-closed');
  _watchEscape(event) {
    if (event.key === 'Escape') {

customElements.define('one-dialog', OneDialog);

const button = document.getElementById('launch-dialog');
button.addEventListener('click', () => {
  document.querySelector('one-dialog').open = true;
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