<style type="text/css">
        body {
            height: 3000px;
        }
        /*回到顶部*/
        #rocket-to-top div {
            left: 0;
            margin: 0;
            overflow: hidden;
            padding: 0;
            position: absolute;
            top: 0;
            width: 149px;
        }

        #rocket-to-top .level-2 {
            background: url("https://images.cnblogs.com/cnblogs_com/xujingyang/1227088/o_o_rocket_button_up.png") no-repeat scroll -149px 0 transparent;
            display: none;
            height: 250px;
            opacity: 0;
            z-index: 1;
        }

        #rocket-to-top .level-3 {
            background: none repeat scroll 0 0 transparent;
            cursor: pointer;
            display: block;
            height: 150px;
            z-index: 2;
        }

        #rocket-to-top {
            background: url("https://images.cnblogs.com/cnblogs_com/xujingyang/1227088/o_o_rocket_button_up.png") no-repeat scroll 0 0 transparent;
            cursor: default;
            display: block;
            height: 250px;
            margin: -125px 0 0;
            overflow: hidden;
            padding: 0;
            position: fixed;
            right: 0;
            top: 80%;
            width: 149px;
            z-index: 11;
        }
    </style>