public/index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Netlify + Nimbella</title>
    <link
      href="https://fonts.googleapis.com/css2?family=Poppins:wght@300&display=swap"
      rel="stylesheet"
    />
    <style>
      .content {
        display: grid;
        place-items: center;
        font-family: 'Poppins', sans-serif;
      }
      h1 {
        font-size: 5rem;
      }
    </style>
  </head>
  <body>
    <div class="content">
      <h1 id="message">Loading...</h1>
    </div>
  </body>

  <script>
    async function main() {
      const greet = await fetch('/api/default/greet?name='); // specify a name, default is World

      document.getElementById('message').innerHTML = (
        await greet.json()
      ).message;
    }

    main().catch(e => console.log(e));
  </script>
</html>