图A显示了我对sm,md和lg设备的设计.在xs设备的情况下,块B应显示在块A上方(如图B所示).但我不知道代码有什么问题.有人请帮助我.
<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap-theme.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
<div class="row">
<div class="col-xs-12 col-sm-3 col-md-2 col-lg-2 col-xs-push-12">A</div>
<div class="col-xs-12 col-sm-6 col-md-8 col-lg-8 col-xs-pull-12">B</div>
<div class="col-xs-12 col-sm-3 col-md-2 col-lg-2">C</div>
</div>
</div>
</body>
</html>
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