bootstrop设置背景图片自适应屏幕

<style type="text/css">
    html{height: 100%;}
    body.aa{height: auto;
    background: url(login-background.png) no-repeat center fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
    color: rgba(255, 255, 255, .95)}
</style>

.bg {
       background:url(图片地址) no-repeat center;
       background-size:contain;
}

<div class="row bg">

.bg {
       background:url(图片地址) no-repeat center fixed;
       background-size:contain;
}