#wallpaper1,
#wallpaper2,
#wallpaper3,
#wallpaper4 {
    position: fixed;
    inset: 0;
    width: 100%;
    height: 100%;
    background-position: center center;
    background-repeat: no-repeat;
    background-size: cover;
    pointer-events: none;
    transition: opacity 1s ease;
    z-index: -1;
}
#wallpaper1 {
    background-image: url("../imgs/bg/1.jpg");
    opacity: 1;
}
#wallpaper2 {
    background-image: url("../imgs/bg/2.jpg");
    opacity: 0;
}
#wallpaper3 {
    background-image: url("../imgs/bg/3.jpg");
    opacity: 1;
}
#wallpaper4 {
    background-image: url("../imgs/bg/4.jpg");
    opacity: 0;
}
.theme {
    position: relative;
    background: transparent;
}