{
  padding: 0;
  margin: 0;
}

body {
  width: 100vw;
  height: 100vh;
}

.worm {
  width: 50px;
  height: 30px;
  background-image: url('worm.gif');
  display: inline-block;
  transform: translateX(-100%);
  animation-name: squirm;
  animation-duration: 5s;
  animation-iteration-count: infinite;
}

@keyframes squirm {
  0% {
    transform: translateX(-100%);
  }
  25% {
    transform: translateX(50vw);
  }
  75% {
    transform: translateX(50vw);
  }
  100% {
    transform: translateX(100vw);
  }
}