How to enable image zoom in fullscreen API mode only?

Question

Codepen Demo Link : https://codepen.io/aghilanbaskar/pen/rNeqMed

I know we need to write a code for zooming option only in Full-screen mode.

Does anyone know how to do it simply by using CSS and JavaScript without any library help.

Javascript Demo Code

I have written a event to listen an image click to open image in full screen API Which is using Full-Screen API to image in full screen

var requestFullscreen = function (ele) {
    if (ele.requestFullscreen) {
        ele.requestFullscreen();
    } else if (ele.webkitRequestFullscreen) {
        ele.webkitRequestFullscreen();
    } else if (ele.mozRequestFullScreen) {
        ele.mozRequestFullScreen();
    } else if (ele.msRequestFullscreen) {
        ele.msRequestFullscreen();
    } else {
        console.log('Fullscreen API is not supported.');
    }
};

var exitFullscreen = function () {
    if (document.exitFullscreen) {
        document.exitFullscreen();
    } else if (document.webkitExitFullscreen) {
        document.webkitExitFullscreen();
    } else if (document.mozCancelFullScreen) {
        document.mozCancelFullScreen();
    } else if (document.msExitFullscreen) {
        document.msExitFullscreen();
    } else {
        console.log('Fullscreen API is not supported.');
    }
};



document.getElementsByTagName('img')[0].addEventListener('click', function(e) {
    e.preventDefault();
    requestFullscreen(this);
});

html {
  font-family: Helvetica, Arial, sans-serif;
  font-size: 100%;
  background: #333;
}

#page-wrapper {
  width: 640px;
  background: #FFFFFF;
  padding: 1em;
  margin: 1em auto;
  border-top: 5px solid #69c773;
  box-shadow: 0 2px 10px rgba(0,0,0,0.8);
}

h1 {
  margin-top: 0;
}

h2 {
    font-size: 0.9em;
    text-transform: uppercase;
    color: #333;
}

hr {
    margin: 1.5em 0;
    border: 0;
    border-top: 1px solid #CCC;
}

button {
  display: inline-block;
  border-radius: 3px;
  border: none;
  font-size: 0.9rem;
  padding: 0.4rem 0.8em;
  background: #69c773;
  border-bottom: 1px solid #498b50;
  color: white;
  -webkit-font-smoothing: antialiased;
  font-weight: bold;
  margin: 0.5em 0.25rem 0;
  text-align: center;
}

button:hover, button:focus {
  opacity: 0.75;
  cursor: pointer;
}

button:active {
  opacity: 1;
  box-shadow: 0 -3px 10px rgba(0, 0, 0, 0.1) inset;
}


img {
    max-width: 640px;
}

img:-webkit-full-screen {
    max-width: none;
}

img:-moz-full-screen {
    max-width: none;
}

img:-ms-fullscreen {
  max-width: none;
}

img:full-screen {
    max-width: none;
}

img:fullscreen {
    max-width: none;
}

<div id="page-wrapper">

    <h1>Fullscreen API Demo</h1>

    <section>
        <h2>Click image to view in Full Screen</h2>
        <img id="image" src="https://ckeditor.com/docs/ckeditor5/latest/assets/img/fields.jpg" alt="Test Image">
    </section>
</div>