使用BootStrap，如果一个Div只占用了一小部分，怎么居中呢？
<!doctype html>
<html >
<head>
<meta charset="utf-8">
<title>BootStrap3.3.2测试</title>
<link href="../bootstrap/3.3.2/css/bootstrap.min.css" target="_blank" rel="external nofollow" rel="stylesheet">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no">
<script src="../Jquery/jquery-1.11.2.min.js"></script>
<script src="../bootstrap/3.3.2/js/bootstrap.min.js"></script>
<style>
.col-center-block {
float: none;
display: block;
margin-left: auto;
margin-right: auto;
}
</style>
</head>
<body>
<div class="container">
<div class="row myCenter">
<div class="col-xs-6 col-md-4 col-center-block">
<form class="form-signin">
<h2 class="form-signin-heading">请登录</h2>
<label for="username" class="sr-only">用户名</label>
<input type="text" id="username" class="form-control" placeholder="用户名" required autofocus>
<label for="inputPassword" class="sr-only">密码</label>
<input type="password" id="inputPassword" class="form-control" placeholder="密码" required>
<div class="checkbox">
<label>
<input type="checkbox" value="remember-me">
记住我 </label>
</div>
<button class="btn btn-lg btn-primary btn-block" type="submit">登录</button>
</form>
</div>
</div>
</div>
</body>
</html>
给Div添加这样一个Style就可以实现：
<style>
.col-center-block {
float: none;
display: block;
margin-left: auto;
margin-right: auto;
}
</style>
最终效果如下：
![响应式前端框架Bootstrap系列（15）面板[图]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)