<div class="header">
  <h1>Search</h1>
  <span></span>
  <input type="text" id="btn-search" class="material-icons" value="search" />
</div>

body {
  font-family: 'Roboto', sans-serif;
  background: #64FFDA;
}

.header {
  display: flex;
  align-items: center;
  padding: 50px;
}
.header h1 {
  font-size: 36px;
  color: #00796B;
}
.header span { flex: 1; }

input[type="text"] {
  border: none;
  background: none;
  
  height: 50px;
  width: 50px;
  
  font-size: 50px;
  color: #00796B;
  text-align: right;
  
  outline: none;
  cursor: pointer;
  transition: width .3s;
}
input[type="text"]:focus {
  font-family: 'Roboto', sans-serif;
  font-size: 24px;
  color: #000;
  text-align: left;
  
  width: 500px;
  height: 10px;
  padding: 20px;
  border-radius: 0;
  background: #fff;    
  box-shadow: 0 2px 10px 0 rgba(0,0,0,.16);
}

input[type="text"]:blur {
  border: none;
  background: none;
  
  height: 50px;
  width: 50px;
  
  font-size: 50px;
  color: #00796B;
  text-align: right;
  
  outline: none;
  cursor: pointer;
  transition: width .3s;
}

var btnSearch = document.getElementById('btn-search');

btnSearch.addEventListener('focus', function() {
  btnSearch.value = '';
});
btnSearch.addEventListener('blur', function() {
  btnSearch.value = 'search';
});