.youtube {
  position:relative;
  width: 100%;
  max-width: 480px;
}

.youtube::before {
  content: "";
  display: block;
  width: 100%;
  padding-top: 56.25%;
}

.youtube iframe{
  position: absolute;
  top: 0;
  right: 0;
  width: 100%;
  height: 100%;
}