examples/testing-dom__responsive-image/responsive-images/picture.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">
    <title>Responsive HTML images demo</title>
    <style>
      html {
        font-family: sans-serif;
        background-color: gray;
      }

      body {
        max-width: 1200px;
        margin: 0 auto;
        background-color: white;
      }

      section {
        padding: 20px;
      }

      p {
        line-height: 1.5;
      }

      img {
        display: block;
        margin: 0 auto;
        max-width: 100%;
      }
    </style>
  </head>
  <body>
    <main>
      <section>
        <h1>My website</h1>

        <picture>
          <source media="(max-width: 799px)" srcset="elva-480w-close-portrait.jpg">
          <source media="(min-width: 800px)" srcset="elva-800w.jpg">
          <img src="elva-800w.jpg" alt="Chris standing up holding his daughter Elva">
        </picture>
      </section>
    </main>
  </body>
</html>