#mainContent{
width:800px;
}

body {
color: #000;
background: url(https://images2015.cnblogs.com/blog/796587/201706/796587-20170625131231788-661258992.jpg
) fixed;
background-size: 1300px;
background-repeat: no-repeat;
font-family: "Helvetica Neue",Helvetica,Verdana,Arial,sans-serif;
font-size: 12px;
min-height: 101%;
}