/*body {
    margin: 0;
    padding: 0;
    background-size: cover;
    background-position: center;
    transition: background-image 1s ease-in-out;
}
*/

#background1, #background2 {
    position: fixed;
    top: 0;
    + left: 0;
    width: 100%;
    height: 100%;
    background-size: cover;
    background-position: center;
    transition: opacity 1s ease-in-out;
    /*transition: background-image 1s ease-in-out;*/
    z-index: -1;
}

#background1 {
    z-index: -2;
}