<form>
  <input type="text" name="search" placeholder="Press here...! Search for example.com">
</form>

input[type=text] {
  width: 130px;
  box-sizing: border-box;
  border: 2px solid #ccc;
  border-radius: 4px;
  font-size: 16px;
  background-color: #007FFF;
  background-image: url('search.png');
  background-position: 10px 10px; 
  background-repeat: no-repeat;
  padding: 12px 20px 12px 40px;
  -webkit-transition: width 0.4s ease-in-out;
  transition: width 0.4s ease-in-out;
color:#fff;
}

input[type=text]:focus {
  width: 100%;
}

<iframe src="https://www.netbax.net/tab/creation/animated-search.html" style="width: 550px; height:550px;" frameborder="0"></iframe>