.container {
  width: 1000px;
  height: 500px;
  border: black solid 2px;
  position: relative;
}

.element {
  background-color: #1e90ff;
  width: 50px;
  height: 50px;
  border-radius: 50%;
  position: absolute;
}

/* animation */
@keyframes move {
  from {
    left: 0;
  }
  to {
    left: 200px;
  }
}

.element {
  animation: move 2s infinite alternate;
}