.livestream{
  margin: auto;
  display: block;
  margin-top: 30px;
  width: 640px;
  height: 360px; 
}

@media screen and (max-width: 479px) {
  .livestream{
    width: 80%;
    margin: auto;
    display: block;
    margin-top: 30px;
  }
}