<template id="dialog-template">
  <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;
    }
  </style>
  <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">Hello world</h1>
      <div id="content" class="content">
        <p>This is content in the body of our modal</p>
      </div>
    </div>
  </div>
</template>

<one-dialog></one-dialog>

<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() {
    super();
    this.close = this.close.bind(this);
    this._watchEscape = this._watchEscape.bind(this);
  }
  
  attributeChangedCallback(attrName, oldValue, newValue) {
    if (oldValue !== newValue) {
      this[attrName] = this.hasAttribute(attrName);
    }
  }
  
  connectedCallback() {
    const template = document.getElementById('dialog-template');
    const node = document.importNode(template.content, true);
    this.appendChild(node);
    
    
    this.querySelector('button').addEventListener('click', this.close);
    this.querySelector('.overlay').addEventListener('click', this.close);
    this.open = this.open;
  }
  
  disconnectedCallback() {
    this.querySelector('button').removeEventListener('click', this.close);
    this.querySelector('.overlay').removeEventListener('click', this.close);
  }
  
  
  get open() {
    return this.hasAttribute('open');
  }
  
  
set open(isOpen) {
    this.querySelector('.wrapper').classList.toggle('open', isOpen);
    this.querySelector('.wrapper').setAttribute('aria-hidden', !isOpen);
    if (isOpen) {
      this._wasFocused = document.activeElement;
      this.setAttribute('open', '');
      document.addEventListener('keydown', this._watchEscape);
      this.focus();
      this.querySelector('button').focus();
    } else {
      this._wasFocused && this._wasFocused.focus && this._wasFocused.focus();
      this.removeAttribute('open');
      document.removeEventListener('keydown', this._watchEscape);
      this.close();
    }
  }
  
  
  close() {
    if (this.open !== false) {
      this.open = false;
    }
    const closeEvent = new CustomEvent('dialog-closed');
    this.dispatchEvent(closeEvent);
  }
  
  _watchEscape(event) {
    if (event.key === 'Escape') {
        this.close();   
    }
  }
}

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

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