输入框焦点
当输入框 input 接收到 :focus 时，输入框的轮廓会被移除，同时应用 box-shadow。
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title>Bootstrap历练实例：表单控件状态(焦点)</title>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width,initial-scale=1.0" />
<link rel="stylesheet" href="bootstrap-3.3.5-dist/css/bootstrap.min.css" />
</head>
<body>
<div class="container">
<form class="form-horizontal" role="form">
<div class="form-group">
<label for="focus" class="control-label col-sm-2">焦点：</label>
<div class="col-sm-10">
<input type="text" id="focus" class="form-control" placeholder="获取焦点" />
</div>
</div>
</form>
</div>
<script src="jQuery/jquery-2.1.4.js"></script>
<script src="bootstrap-3.3.5-dist/js/bootstrap.min.js"></script>
</body>
</html>