how to fill the screen with a div tag in html code example

Example 1: javascript full screen div

$('#toggle_fullscreen').on('click', function(){
  // if already full screen; exit
  // else go fullscreen
  if (
    document.fullscreenElement ||
    document.webkitFullscreenElement ||
    document.mozFullScreenElement ||
    document.msFullscreenElement
  ) {
    if (document.exitFullscreen) {
      document.exitFullscreen();
    } else if (document.mozCancelFullScreen) {
      document.mozCancelFullScreen();
    } else if (document.webkitExitFullscreen) {
      document.webkitExitFullscreen();
    } else if (document.msExitFullscreen) {
      document.msExitFullscreen();
    }
  } else {
    element = $('#container').get(0);
    if (element.requestFullscreen) {
      element.requestFullscreen();
    } else if (element.mozRequestFullScreen) {
      element.mozRequestFullScreen();
    } else if (element.webkitRequestFullscreen) {
      element.webkitRequestFullscreen(Element.ALLOW_KEYBOARD_INPUT);
    } else if (element.msRequestFullscreen) {
      element.msRequestFullscreen();
    }
  }
});
#container{
  border:1px solid red;
  border-radius: .5em;
  padding:10px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="container">
  <p>
    <a href="#" id="toggle_fullscreen">Toggle Fullscreen</a>
  </p>
  I will be fullscreen, yay!
</div>

Example 2: full screen a div

$('#toggle_fullscreen').on('click', function(){
  // if already full screen; exit
  // else go fullscreen
  if (
    document.fullscreenElement ||
    document.webkitFullscreenElement ||
    document.mozFullScreenElement ||
    document.msFullscreenElement
  ) {
    if (document.exitFullscreen) {
      document.exitFullscreen();
    } else if (document.mozCancelFullScreen) {
      document.mozCancelFullScreen();
    } else if (document.webkitExitFullscreen) {
      document.webkitExitFullscreen();
    } else if (document.msExitFullscreen) {
      document.msExitFullscreen();
    }
  } else {
    element = $('#container').get(0);
    if (element.requestFullscreen) {
      element.requestFullscreen();
    } else if (element.mozRequestFullScreen) {
      element.mozRequestFullScreen();
    } else if (element.webkitRequestFullscreen) {
      element.webkitRequestFullscreen(Element.ALLOW_KEYBOARD_INPUT);
    } else if (element.msRequestFullscreen) {
      element.msRequestFullscreen();
    }
  }
});