section.banner .banner-container
{

}
  section.banner .banner-container .banner-item
  {
    background-size: cover;
    background-repeat: no-repeat;
    background-position: center;
    height: 33.33333vw;
  }

@media(max-width: 768px)
{
  section.banner .banner-container .banner-item
  {
    height: 300px;
  }
}