css

@keyframes test {
  0%  {border-color: darkgreen;}
  50%  {border-color: red;}
  70%  {border-color: yellow;}
  100% {border-color: grey;}
}

p {
  width: 400px;
  height: 200px;
  border: solid yellow 20px;
  background-color: black;
  animation-name: test;
  animation-duration: 15s;
  animation-iteration-count: infinite;
  animation-direction: alternate;



}