JSFiddle - React, Tailwind, and code Playground

HTML

<div class="block">
  
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</div>

CSS

.block {
  width: 100%;
  height: 50px;
  background-color: lightgreen;
  display: flex;
  justify-content: space-between;
  align-items: center;
  animation: anim 3s infinite;
}


@keyframes anim {
  
  0% {
    width: 100%;
  }
  
  30% {
    width: 60%;
  }
  
  60% {
    width: 30%;
  }
  
  100% {
    width: 100%;
  }
  
}