.container{
    width: 100%;
    height: 400px;
    background:red;
}


body{
background:black;

}

html,body{
   margin: 0px;
   padding: 0px;
}

body {margin:0px;background:#000;}
.container{
    width: 100%;
    min-height: 400px;
    background:red;padding:0px;
}