anchor.diff:      document.getElementById('btn-back').addEventListener('click', function(){
         clickNumber -= 1;
         size_ = size_screen*clickNumber;
  +
         // optimizar
         if (clickNumber < 1) {
           document.getElementById('btn-back').style.display = 'none';
  
positive.code:     </div>
    </div>
  </div>
  
  <div class="video">
    <span id="close-video-tag">X</span>
    <video id="tag-video" src="http://thesocialus.com/video1.mp4" autoplay poster="/assets/preload_image.png" width="100%" height='100%'></video>
  
negative.code:     position: fixed;
    }
  
    .section-content{
      height: 100vh;
      width: 100vw;
  