<div class="video-container"><iframe src="https://www.youtube.com/embed/XXXXXXXXXXX?rel=0&start=0&end=" allowfullscreen></iframe></div> code example

Example: responsive youtube embed html

//Add the following CSS to your code


.iframe-container{
  position: relative;
  width: 100%;
  padding-bottom: 56.25%; 
  height: 0;
}
.iframe-container iframe{
  position: absolute;
  top:0;
  left: 0;
  width: 100%;
  height: 100%;
}