CSS实现鼠标悬停遮罩效果

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, minimum-scale=1.0, maximum-scale=1.0">
    <title>Bootstrap鼠标悬停图片遮罩特效</title>

    <link href="/css/demo.css" rel="stylesheet" media="all" />

    <!--[if IE]>

    <style type="text/css">
        li.remove_frame a {
            padding-top: 5px;
            background-position: 0px -3px;
        }
    </style>

    <![endif]-->
    <script src="/js/jquery-1.11.1.min.js"></script>
    <script type="text/javascript" src="/js/jquery.qrcode.min.js"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            function fixHeight() {
                var headerHeight = $("#switcher").height();
                $("#iframe").attr("height", $(window).height() - 54 + "px");
            }
            $(window).resize(function () {
                fixHeight();
            }).resize();

            $('.icon-monitor').addClass('active');

            $(".icon-mobile-3").click(function () {
                $("#by").css("overflow-y", "auto");
                $('#iframe-wrap').removeClass().addClass('mobile-width-3');
                $('.icon-tablet,.icon-mobile-1,.icon-monitor,.icon-mobile-2,.icon-mobile-3').removeClass('active');
                $(this).addClass('active');
                return false;
            });

            $(".icon-mobile-2").click(function () {
                $("#by").css("overflow-y", "auto");
                $('#iframe-wrap').removeClass().addClass('mobile-width-2');
                $('.icon-tablet,.icon-mobile-1,.icon-monitor,.icon-mobile-2,.icon-mobile-3').removeClass('active');
                $(this).addClass('active');
                return false;
            });

            $(".icon-mobile-1").click(function () {
                $("#by").css("overflow-y", "auto");
                $('#iframe-wrap').removeClass().addClass('mobile-width');
                $('.icon-tablet,.icon-mobile,.icon-monitor,.icon-mobile-2,.icon-mobile-3').removeClass('active');
                $(this).addClass('active');
                return false;
            });

            $(".icon-tablet").click(function () {
                $("#by").css("overflow-y", "auto");
                $('#iframe-wrap').removeClass().addClass('tablet-width');
                $('.icon-tablet,.icon-mobile-1,.icon-monitor,.icon-mobile-2,.icon-mobile-3').removeClass('active');
                $(this).addClass('active');
                return false;
            });

            $(".icon-monitor").click(function () {
                $("#by").css("overflow-y", "hidden");
                $('#iframe-wrap').removeClass().addClass('full-width');
                $('.icon-tablet,.icon-mobile-1,.icon-monitor,.icon-mobile-2,.icon-mobile-3').removeClass('active');
                $(this).addClass('active');
                return false;
            });
        });
    </script>

    <script type="text/javascript">
        function Responsive($a) {
            if ($a == true) $("#Device").css("opacity", "100");
            if ($a == false) $("#Device").css("opacity", "0");
            $('#iframe-wrap').removeClass().addClass('full-width');
            $('.icon-tablet,.icon-mobile-1,.icon-monitor,.icon-mobile-2,.icon-mobile-3').removeClass('active');
            $(this).addClass('active');
            return false;
        };
    </script>   

</head>
<body id="by">

    <div id="switcher">
        <div class="center">
            <ul>
                <div id="Device">
                    <li class="device-monitor"><a href="javascript:">
                        <div class="icon-monitor"></div>
                    </a></li>
                    <li class="device-mobile"><a href="javascript:">
                        <div class="icon-tablet"></div>
                    </a></li>
                    <li class="device-mobile"><a href="javascript:">
                        <div class="icon-mobile-1"></div>
                    </a></li>
                    <li class="device-mobile-2"><a href="javascript:">
                        <div class="icon-mobile-2"></div>
                    </a></li>
                    <li class="device-mobile-3"><a href="javascript:">
                        <div class="icon-mobile-3"></div>
                    </a></li>
                </div>
                <li class="top2">
                    <a href="javascript:void(0)">手机二维码预览</a>
                    <div class="vm">
                        <div id="output"></div>
                        <p style="color: #808080; margin: 10px 0 0 0;">扫一扫，直接在手机上打开</p>
                    </div>
                </li>
                <li class="logoTop">
                    <a href="/script/content/1788">Bootstrap鼠标悬停图片遮罩特效</a>
                    <script type="text/javascript">
                        jQuery('#output').qrcode({ width: 150, height: 150, text: window.location.href });
                    </script>
                    <li class="remove_frame"><a href="/temp/201803/Bootstrap鼠标悬停图片遮罩特效/index.html" title="移除框架"></a></li>
            </ul>
        </div>
    </div>

    <div id="iframe-wrap">
        <iframe id="iframe" src="/temp/201803/Bootstrap鼠标悬停图片遮罩特效/index.html" frameborder="0" width="100%"></iframe>
    </div>


    <div id="footer-notice" class="kj_bottom">
        <div style="width: 900px; margin: 0 auto">
            <p class="left cut">
                <span>名称：</span>
                <a href="/script/content/1788" class="down">Bootstrap鼠标悬停图片遮罩特效</a>
                <span>标签：</span><a href='/script/tags?key=图片'>图片</a><a href='/script/tags?key=bootstrap'>bootstrap</a>
            </p>
            <div class="clear"></div>
        </div>
    </div>
</body>
</html>