Adds parent headings to subheadings - https://lukasznojek.com/blog/2019/08/automatically-enhance-headers-with-hierarchy-and-links/

addParentHeadings.js

/**
 * Enhances headers with names of parent headers
 * If you have h2: 'abc' and h3: 'def', then h3 will be displayed as 'abc > def'
 *
 * @param {string} sectionSelector - id or class of the section that contains the headings, e.g. '#main'
 * @param {number[]} headings - array of heading numbers that should be changed, in the order of processing, e.g.:
 *   [4, 3] -> for h4 show h3, for h3 show h2
 *   [3, 4] -> for h3 show h2, for h4 show h3 with h2
 * @param {string} separator - the text between parent and child commit, by default it's '>'
 * @param jQuery - reference to the jQuery
 *
 * Style the result in .prev-title, e.g.:
 *   span.prev-title {
 *     opacity: 0.5;
 *     font-size: 90%;
 *   }
 */
function addParentHeadings(sectionSelector, headings, separator = ' > ', jQuery = $) {
	headings.forEach(function(level) {
		jQuery(sectionSelector + ' h' + level).each(function() {
			const $this = jQuery(this);
			const prev = $this.prevAll('h' + (level-1)).first().text();
			$this.html('<span class="prev-title">' + prev + separator + '</span>' + $this.html());
		});
	});
}

style.css

span.prev-title {
	opacity: 0.5;
	font-size: 90%;
}