index.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Dark Color Generator</title>
  <style>
    body {
      margin: 0;
      font-family: 'Arial', sans-serif;
    }
    main {
      height: 100vh;
      transition: background 1s;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 2em;
      box-sizing: border-box;
      text-align: center;
    }
    h1 {
      margin: 0;
      font-weight: 400;
      color: #fff;
      transition: color 1s;
      line-height: 2;
    }
    footer {
      text-align: center;
      padding: 0.5rem 0;
      background-color: #eaeaea90;
    }
    footer p {
      font-size: 0.75rem;
      margin: 0.25rem 0;
      color: #221133;
    }
    footer a {
      text-decoration: none;
      color: inherit;
    }
  </style>
</head>
<body>
  <main id="background">
    <h1 id="header">
      Generate Random Dark Colors with JavaScript
    </h1>
  </main>
  <script>
    const background = document.getElementById("background");
    const h1 = document.getElementById("header");

    const getRandomNumber = (min, max) => {
      return Math.floor(Math.random() * (max - min +1)) + min;
    };

    const hslToHex = (h, s, l) => {
      l /= 100;
      const a = s * Math.min(l, 1 - l) / 100;
      const f = n => {
        const k = (n + h / 30) % 12;
        const color = l - a * Math.max(Math.min(k - 3, 9 - k, 1), -1);
        return Math.round(255 * color).toString(16).padStart(2, '0');
      };
      return `#${f(0)}${f(8)}${f(4)}`;
    };

    const setBackgroundColor = () => {
      const h = getRandomNumber(0, 360);
      const s = getRandomNumber(30, 80);
      const randomColor = `hsl(${h}deg, ${s}%, 50%)`;

      background.style.backgroundColor = randomColor;
      background.style.color = randomColor;
      h1.innerHTML = hslToHex(h, s, 50) + "<br />" + randomColor;
    };

    setBackgroundColor();

    setInterval(() => {
      setBackgroundColor();
    }, 3000);
  </script>
</body>
</html>