* {
  margin: 0;
  padding: 0;
}

#box {
  position: relative;
  font-size: 150px;
  width: 400px;
  height: 400px;
  margin: 50px auto;
  border: 5px solid #ffb787;
  border-radius: 5%;
  overflow: hidden;
}

#box .font {
  line-height: 200px;
  text-align: center;
  width: 200px;
  height: 200px;
  color: red;
  float: left;
}

#box .bg {
  position: absolute;
  width: 200px;
  height: 200px;
  background: red;
  animation: bg-move 3s infinite linear;
}

@keyframes bg-move {
  0% {
    transform: translateX(0) translateY(0)
  }

  25% {
    transform: translateX(200px)
  }

  50% {
    transform: translateX(200px) translateY(200px)
  }

  75% {
    transform: translateX(0) translateY(200px)
  }

  100% {
    transform: translateX(0) translateY(0)
  }
}

.po1,
.po2,
.po3,
.po4 {
  overflow: hidden;
  position: absolute;
  background: red;
  width: 0;
  height: 0;
}

.po1 {
  right: 200px;
  bottom: 200px;
  animation: w-h 2s 0.5s infinite linear;
}

.po2 {
  left: 200px;
  bottom: 200px;
  animation: w-h 2s infinite linear reverse;
}

.po3 {
  right: 200px;
  top: 200px;
  animation: w-h 2s 1s infinite linear reverse;
}

.po4 {
  left: 200px;
  top: 200px;
  animation: w-h 2s 1.5s infinite linear;
}

.po1 div,
.po2 div,
.po3 div,
.po4 div {
  position: absolute;
  width: 200px;
  text-align: center;
  color: #fff;
}

.po1 div {
  bottom: 0;
  right: 0;
}

.po2 div {
  bottom: 0;
  left: 0;
}

.po3 div {
  right: 0;
  top: 0;
}

.po4 div {
  top: 0;
  left: 0;
}



@keyframes w-h {
  0% {
    height: 0;
    width: 200px;
  }

  25% {
    height: 200px;
    width: 200px;
  }

  50% {
    height: 200px;
    width: 0;
  }
}