hallmonitor.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Hall Monitor</title>
  </head>
  <body>
    <button id="fullscreen">Click to open</button>
    <button id="random">Randomise colour</button>
    <script>
      const randomiseColor = () => {
        const hue = Math.random() * 360
        document.documentElement.style.backgroundColor = `hsl(${hue},100%,50%)`
      }

      const openButton = document.getElementById('fullscreen')
      openButton.addEventListener('click', () => {
        document.documentElement.requestFullscreen()
        openButton.style.display = 'none'
      })

      const randomButton = document.getElementById('random')
      randomButton.addEventListener('click', randomiseColor)

      setInterval(randomiseColor, 1000 * 60 * 60)
    </script>
  </body>
</html>