countdown timer; display fullscreen for speakers at conferences

Countdown

<style>
  body {
    background-color: black;
    color: white;
    font-family: sans-serif;
    text-align: center;
  }
  #minutes {
    font-size: 500px;
  }
  #seconds {
    font-size: 100px;
  }
</style>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js"></script>
<script>
  $(function() {
    
    // Change me!!!
    var seconds = 25 * 60;
    // Change me!!!
    
    setInterval(function() {
      seconds--;
      
      if (seconds < (3 * 60))
      {
        $('body').css('background-color', 'red');
        $('body').css('color', 'black');
      }
      else if (seconds < (5 * 60))
      {
        $('body').css('background-color', 'yellow');
        $('body').css('color', 'black');        
      }
        
      $("#minutes").html(Math.floor(seconds/60));
      var secs = seconds % 60;
      
      $("#seconds").html((secs < 10) ? '0'+secs : secs );
    }, 1000);
  });
</script>

<!-- Change the values here and in the javascript above -->
<div id='minutes'>25</div>
<div id='seconds'>00</div>