Demo: CSS min-width

<div class='container'>
  <div class='box'>Resize me!</div>
</div>

.container {
  width: 100%;
  background-color: #f0f0f0;
  padding: 20px;
}

.box {
  min-width: 200px;
  width: 100%;
  background-color: #4CAF50;
  color: white;
  padding: 20px;
  text-align: center;
  border: 2px solid #388E3C;
  transition: width 0.3s;
}

.box:hover {
  width: 300px;
}

// No JavaScript required for this demo