<link href="//netdna.bootstrapcdn.com/bootstrap/3.1.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//netdna.bootstrapcdn.com/bootstrap/3.1.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<div class="demo">
<div class="calculator">
<div class="screen"><input type="text" /></div>
<div class="keypad">
<div class="keys">
<button type="button" class="btn btn-info btn-xs">7</button>
<button type="button" class="btn btn-info btn-xs">8</button>
<button type="button" class="btn btn-info btn-xs">9</button>
<button type="button" class="btn btn-info btn-xs">÷</button>
</div>
<div class="keys">
<button type="button" class="btn btn-info btn-xs">4</button>
<button type="button" class="btn btn-info btn-xs">5</button>
<button type="button" class="btn btn-info btn-xs">6</button>
<button type="button" class="btn btn-info btn-xs">×</button>
</div>
<div class="keys">
<button type="button" class="btn btn-info btn-xs">1</button>
<button type="button" class="btn btn-info btn-xs">2</button>
<button type="button" class="btn btn-info btn-xs">3</button>
<button type="button" class="btn btn-info btn-xs">-</button>
</div>
<div class="keys">
<button type="button" class="btn btn-info btn-xs">0</button>
<button type="button" class="btn btn-info btn-xs">C</button>
<button type="button" class="btn btn-info btn-xs">=</button>
<button type="button" class="btn btn-info btn-xs">+</button>
</div>
</div>
</div>
