(function() {
const doc = document.documentElement;
const thumb = document.querySelector('.custom-scrollbar .scroll-thumb');
const track = document.querySelector('.custom-scrollbar .scroll-track');
function updateThumb() {
const maxScroll = doc.scrollHeight - doc.clientHeight;
const trackLen = track.clientHeight;
// If nothing to scroll, thumb should fill the track
if (maxScroll <= 0) {
thumb.style.height = trackLen + 'px';
thumb.style.top = '0px';
return;
}
// Otherwise size & position proportionally
const h = Math.max((doc.clientHeight / doc.scrollHeight) * trackLen, 20);
const t = (doc.scrollTop / maxScroll) * (trackLen - h);
thumb.style.height = h + 'px';
thumb.style.top = t + 'px';
}
window.addEventListener('load', updateThumb);
window.addEventListener('scroll', updateThumb, { passive: true });
window.addEventListener('resize', updateThumb);
})();
