body{padding:0;margin:0;height:100%}.cover{position:absolute;top:0;left:0;padding:0;margin:0;width:100%;height:100%;min-width:400px;min-height:600px;background:url("../images/bg.jpg") no-repeat scroll 50% 50%/cover transparent}.login-form{display:block;color:#fff;width:500px;height:300px;margin-left:auto;margin-right:auto;margin-top:150px;padding:20px;background:rgba(0,0,0,0.7);border-radius:15px}