.back:hover{
  animation: rotation 2.5s infinite linear;
}

@keyframes rotation {
  0% {
    transform: rotate(-50deg);
  }
  50% {
    transform: rotate(50deg);
  }
  100% {
    transform: rotate(-50deg);
  }
}
.main{
  background: transparent;
  width: 990px;
  height: 730px;
  padding: 10px;
  margin: 1px;
  position: absolute;
  left: 125px;
  top: 50px;
}
.rec1{
  width:970px;
  height:450px;
  background: transparent;
  margin: 50px;
  transform: rotate(-5deg);
}