body {
  background: #2e2e2e;
}

#gradation {
  box-sizing: border-box;
  position: absolute;
  top: 0; bottom: 0;
  left: 0; right: 0;
  border: solid #2e2e2e 10px;
  background: linear-gradient(90deg, #54c9c2, #b0dea6);
  overflow: hidden;
}

.box {
  position: absolute;
  top: 0; bottom: 0;
  margin: auto -100px;
  border-radius: 50%;
  width: 200px; height: 200px;
  background: linear-gradient(90deg, #54c9c2, #b0dea6) center center;
  background-size: 100vw 100vh;
}

.b1 {
  top: 0;
  animation: lr 5s ease-in-out infinite alternate;
}

.b2 {
  bottom: 0;
  animation: rl 5s ease-in-out infinite alternate;
}

@keyframes lr {
  0% {
    left: 0%;
  }

  100% {
    left: 100%;  
  }
}

@keyframes rl {
  0% {
    right: 0%;
  }

  100% {
    right: 100%;  
  }
}