<div class="container">
  <div class="box"></div>
  <div class="box"></div>
  <div class="box"></div>
</div>

.container {
  position: relative;
  width: 100%;
  height: 100vh;
  overflow: hidden;
}

.box {
  position: absolute;
  width: 100px;
  height: 100px;
  background-color: #ff0000;
  animation: move 5s infinite linear;
}

@keyframes move {
  0% {
    left: 0;
  }
  100% {
    left: calc(100% - 100px);
  }
}