.wrapper {
  width: 100%;
  display: block;
  position: relative;
}
.wrapper:after {
  padding-top: 56.25%;
  display: block;
  content: '';
}
.main {
  position: absolute;
  top: 0;
  bottom: 0;
  right: 0;
  left: 0;
  background-color: red;
  color: white;
}