in _static/js/theme.js [1113:1124]
$(article).each(function (i) {
var offsetScroll = $(this).offset().top - $(window).scrollTop();
if (
offsetScroll <= topMenuHeight + 200 &&
offsetScroll >= topMenuHeight - 200 &&
scrollItems[i] == "#" + $(this).attr("id") &&
$(".hidden:visible")
) {
$(menuItems).removeClass("side-scroll-highlight");
$(menuItems[i]).addClass("side-scroll-highlight");
}
});