html, body {
    height: 100%;
    margin: 0;
}

.bg {
    position: fixed;
    top: 0; left: 0;
    width: 100vw; height: 100vh;
    overflow: hidden;
    z-index: -1; /* behind content */
    display: flex;
    flex-direction: column;
}

.half {
    width: 100vw;
    height: 50vh;
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
}

.half-top {
    background-image: url('mobile_top.webp');
    background-position: bottom;
}

.half-bottom {
    background-image: url('mobile_bottom.webp');
    background-position: top;
}

@media (min-width: 992px) {
    .half-top {
        background-image: url('desktop_top.webp');
    }
    .half-bottom {
        background-image: url('desktop_bottom.webp');
    }
}

.messenger-btn {
    position: fixed;
    top: 0; left: 0; width: 100vw; height: 100vh;
    z-index: 9999;
    opacity: 0;
    cursor: pointer;
}