1 设置背景图片的两种方式：

方式一： <img src="https://blog.csdn.net/qq_34328404/article/img/10.jpg"/ class="back" id="Background">

.back{
position: fixed;
width: 100%;
height: 100%;
display: block;
z-index: -100;
}

方式二：div class="body" id="Background"></div>

.body{
width: 100%;
height: 100%;
position: fixed;
z-index: -10;
background-image: url(https://blog.csdn.net/qq_34328404/article/img/10.jpg);
background-repeat: no-repeat;
background-position: 0px 0px;
background-size: 100% 100%;
}

2 解决手机端背景图片自适应问题

("#Background").height($("#Background").height());
});