<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<div class="col-md-6">
<div style="padding:40px;background: red;">
<div class="input-group">
<input type="text" class="form-control" placeholder="Recipient's username" aria-describedby="basic-addon2">
<span class="input-group-addon" id="basic-addon2" style=" background: blue;color: #fff;cursor: pointer;" >@example.com</span>
</div>
</div>
</div>
