body{
background-color:#efefef;
 background: url(https://images.cnblogs.com/cnblogs_com/Ronchi-Zhang/1847521/o_2009141409560e26ca2e82c97f16aa3fb4f8ede9fc24.jpg) center/cover no-repeat;
background-repeat:no-repeat;
background-attachment:fixed;
background-position:center 0;
background-size:cover;
background-top:0px;
opacity:0.9;
}