$(window).on('load', function() {
    $(window).on("scroll touchmove", function () {
        $('.wrapper').toggleClass('tiny', $(document).scrollTop() > 0);
    });
});

.wrapper {
    grid-template-rows: 80px calc(75vh - 80px) 25vh 80px;
    -o-transition: all 0.5s;
    -moz-transition: all 0.5s;
    -webkit-transition: all 0.5s;
    transition: all 0.5s;
}
.tiny {
    grid-template-rows: 40px calc(75vh - 40px) 25vh 80px;
}