So you have some long blog posts and you want to give some indication to your readers who long it is and how much more they have to go. With a site leve html block with the following code, you can add a scroll progress indicator every page on your site. Or you can add the code to an individual page
Add an html block with the following content at the site level.
let wintop = $(window).scrollTop(), docheight =
$(document).height(), winheight = $(window).height();
let scrolled = (wintop/(docheight-winheight))*100;
$('#scroll-indicator').css('width',(scrolled + '%'));