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

@import url("https://fonts.googleapis.com/css2?family=Exo:wght@600&display=swap");

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  width: 100vw;
  min-height: 100vh;

  display: flex;
  justify-content: center;
  align-items: center;
  gap: 40px;

  font-family: "Exo", Arial, sans-serif;
  background-color: #151522;
  color: #fff;
  place-content: center;
  padding: 10px;
}

.box {
  width: 50px;
  height: 50px;
  --offset: 0;
  transform: translateX(var(--offset));
  border-radius: 5px;
  background-color: #09f;
  animation: moveBox 2s linear infinite;
}

@keyframes moveBox {
  0% {
    --offset: 0;
  }
  50% {
    --offset: 300px;
  }
  100% {
    --offset: 600px;
  }
}