body{
margin: 0px 10px 5px 10px;
/* background-color:#191970; */
background-repeat:no-repeat;
background-attachment:fixed;
background-size:contain;
background-position:center center
}

#second_screen {
margin: 0 auto;
height: 100%; 
}

#toBack {
    display: block;
    cursor: pointer;
    width: 100px;
    text-align: center;
    padding: 5px;
    position: fixed;
    bottom:10px;
    left: -15px;
    cursor: pointer;
    color: #300;
    text-decoration: none;
    z-index: 100;
}
HTML, body { 
 width: 100%; 
 height: 100%; 
 }