<div id="wrap">

  <!-- section -->
  <div class="section">
    <div class="center">

      <button id="go">Фулскрин</button>

    </div>
  </div>
  <!--/section -->

</div>

html,
body {
  margin: 0;
  padding: 0;
  font-family: sans-serif;
  font-size: 16px;
  line-height: 1.4;
  color: #555;
  background: #fff;
}

* {
  box-sizing: border-box;
}

#wrap {
  position: relative;
}

.section {
  padding: 40px;
}

#line {
  font-size: 24px;
  margin-bottom: 20px;
}

#go {
  padding: 20px;
  cursor: pointer;
}

var goBtn = document.getElementById('go');

goBtn.onclick = function () {
  document.documentElement.requestFullscreen();
}

goBtn.onclick = function () {
  launchFullScreen(document.documentElement);
}

function launchFullScreen(element) {

  if (element.requestFullScreen) {
    element.requestFullScreen();
  } else if (element.mozRequestFullScreen) {
    element.mozRequestFullScreen();
  } else if (element.webkitRequestFullScreen) {
    element.webkitRequestFullScreen();
  }
}