the transition is immediate.">
<style>
  div {
    height: 100px;
    transition-property: width;
    transition-timing-function: linear;
    width: 100px;
  }
  #ref1 {
    background-color: yellow;
    transition-duration: 2s;
  }
  #ref2 {
    background-color: gray;
    transition-duration: 0s;
  }
  #test {
    background-color: blue;
  }
</style>
<body>
  <p>Click the 'Start' button below. Test passes if the width of yellow square grows smoothly but the gray and blue grow immediately.</p>
  <div id="r