element.style {
}
body{
    background-image: url("https://images.cnblogs.com/cnblogs_com/Star-dust/1060972/o_%E6%98%9F%E5%B0%98.jpg");
    background-repeat: no-repeat;
    background-attachment: fixed;
            background: url(https://images.cnblogs.com/cnblogs_com/Star-dust/1060972/o_%E6%98%9F%E5%B0%98.jpg) no-repeat center center fixed; 

            background-size: 100%;//此处要注意，可以填cover也可以填100%。建议填100%
       
}
div#blogTitle {
    height: 76px;
    padding: 0;
    background: rgba(255,255,255,0.7);
}
#sideBar {
    border: 1px solid #ced7ce;
    border-right: 3px solid #ced7ce;
    border-bottom: 3px solid #ced7ce;
    position: absolute;
    top: 86px;
    left: 8px;
    background: #fff;
    padding: 0;
    width: 280px;
    background: rgba(255,255,255,0.7);
}
#mainContent {
    margin-left: 300px;
    margin-right: 5px;
    background: rgba(255,255,255,0.1);
    margin-top: 10px;
}
div.forFlow {
    border: 1px solid #ced7ce;
    border-right: 3px solid #ced7ce;
    border-bottom: 3px solid #ced7ce;
    background: #fff;
    padding: 45px 37px 40px;
    margin-left: 0;
    left: 0;
    background: rgba(255,255,255,0.7);
}