<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="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<div class="container">
<div class="row">
<h2>Bootstrap 3 input group and wells</h2>
<div class="input-group input-group-lg">
<span class="input-group-addon" id="sizing-addon1">@</span>
<input type="text" class="form-control" placeholder="Username" aria-describedby="sizing-addon1">
</div>