slides_before_body.html

<script>
const availableSlides = [...document.querySelectorAll('section[id]')].map((element) => '#' + element.id);
availableSlides.unshift('#');

function goToSlide(number) {
    if (availableSlides[number]) {
        location = availableSlides[number];
    }
}

document.addEventListener('keydown', function(event) {
    const currentSlide = availableSlides.findIndex((availableSlide) => availableSlide === (location.hash || '#'));

    switch (event.key) {
        case 'ArrowLeft':
            goToSlide(currentSlide - 1);
            break;
        case 'ArrowRight':
            goToSlide(currentSlide + 1);
            break;
    }
});
</script>