html,
body {
  height: 100%;
}

.mydiv {
  width:100%;
  height:100%;
  color:black;
  font-weight:bold;
  animation: myanimation 10s infinite;
}

@keyframes myanimation {
  0% {background-color: #2197E5;}
  25%{background-color:#8CC1E4;}
  50%{background-color:#73B4DF;}
  75%{background-color:#52A8E1  ;}
  100% {background-color: #2197E5;}
}