<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-12 col-sm-12 col-xs-8 " style="background:#fff; padding:30px;">
<div class="col-md-6 col-sm-6 col-xs-12">
<h3 class="text-center">Billing Address</h3>
<hr>
<div class="col-xs-6 col-sm-6 col-md-6">
<div class="form-group">
<input type="text" name="first_name" id="first_name" class="form-control input-sm" placeholder="First Name">
</div>
</div>
<div class="col-xs-6 col-sm-6 col-md-6">
<div class="form-group">
<input type="text" name="last_name" id="last_name" class="form-control input-sm" placeholder="Last Name">
</div>
</div>
<div class="col-xs-6 col-sm-6 col-md-6">
<div class="form-group">
<input type="text" name="first_name" id="first_name" class="form-control input-sm" placeholder="Email id">
</div>
</div>
<div class="col-xs-6 col-sm-6 col-md-6">
<div class="form-group">
<input type="text" name="last_name" id="last_name" class="form-control input-sm" placeholder="Mobile no">
</div>
</div>
<div class="col-xs-12 col-sm-12 col-md-12">