Dymok

gulp.task("serve", function () {
    browserSync.init({
        server: "dev"
    });

    gulp.watch("src/scss/*.scss", ["dev:scss"]);
    gulp.watch("src/**/*.html", ["dev:html"]);
    gulp.watch("src/js/*.js", ["dev:js"]);
    gulp.watch("src/js/libs/*.js", ["dev:js-libs"]);
    gulp.watch("dev/*.html").on("change", browserSync.reload);
    gulp.watch("dev/js/*.js").on("change", browserSync.reload);
    gulp.watch("dev/**/*.css").on("change", browserSync.reload);
});

display: flex;
flex-direction: column;

$(window).scroll(function() {
    var top = $(document).scrollTop();
    if (top < 300) $(".top_nav").removeClass('fixed');
    else $(".top_nav").addClass('fixed');
});

.fixed{
  position: fixed;
}

@media screen and (max-width: 575px) {
  .grid-item {
    left: 50% !important;
    transform: translateX(-50%);
  }
}