Tips and tricks

open the console / devtools and enter

// Create a class for the element
class PopUpInfo extends HTMLElement {
  constructor() {
    // Always call super first in constructor
    super();

    // Create a shadow root
    const shadow = this.attachShadow({mode: 'open'});

    // Create spans
    const wrapper = document.createElement('span');
    wrapper.setAttribute('class', 'wrapper');

    const icon = document.createElement('span');
    icon.setAttribute('class', 'icon');
    icon.setAttribute('tabindex', 0);

    const info = document.createElement('span');
    info.setAttribute('class', 'info');

    // Take attribute content and put it inside the info span
    const text = this.getAttribute('data-text');
    info.textContent = text;

    // Insert icon
    const img = document.createElement('img');
    img.src = this.hasAttribute('img') ? this.getAttribute('img') : 'img/default.png';
    icon.appendChild(img);

    // Create some CSS to apply to the shadow dom
    const style = document.createElement('style');
    console.log(style.isConnected);

    style.textContent = `
      .wrapper {
        position: relative;
      }
      .info {
        font-size: 0.8rem;
        width: 200px;
        display: inline-block;
        border: 1px solid black;
        padding: 10px;
        background: white;
        border-radius: 10px;
        opacity: 0;
        transition: 0.6s all;
        position: absolute;
        bottom: 20px;
        left: 10px;
        z-index: 3;
      }
      img {
        width: 1.2rem;
      }
      .icon:hover + .info, .icon:focus + .info {
        opacity: 1;
      }
    `;

    // Attach the created elements to the shadow dom
    shadow.appendChild(style);
    console.log(style.isConnected);
    shadow.appendChild(wrapper);
    wrapper.appendChild(icon);
    wrapper.appendChild(info);
  }
}

// Define the new element
customElements.define('popup-info', PopUpInfo);

Then, you can just enter:

document.body.insertAdjacentHTML('beforeend', `<popup-info
  img="https://i.imgur.com/5TdEqBr.png"
  data-text="Your card validation code (CVC) is an extra security feature — it is the last 3 or 4 numbers on the back of your card.">`);