.bg {
  width: 100%;
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background-size: 300% 300%;
  background-image: linear-gradient(-45deg, yellow 0%, yellow 25%, yellow 51%, #ff357f 100%);
  -webkit-animation: AnimateBG 20s ease infinite;
          animation: AnimateBG 20s ease infinite;
}

@-webkit-keyframes AnimateBG {
  0% {
    background-position: 0% 50%;
  }
  50% {
    background-position: 100% 50%;
  }
  100% {
    background-position: 0% 50%;
  }
}

@keyframes AnimateBG {
  0% {
    background-position: 0% 50%;
  }
  50% {
    background-position: 100% 50%;
  }
  100% {
    background-position: 0% 50%;
  }
}