linqpad html export toggle script.html

<script>
	// loop over all "up-down" elements
	for(let ud of document.querySelectorAll('span[id$=ud]'))
	{
		// reflect that it is already expanded
		ud.className = 'arrow-up';

		// derive the expandable element's id
		let id = ud.id.substring(0, ud.id.length - 2);

		// collapse everything
		toggle(id);

		// add click handler for toggling
		ud.addEventListener('click', e => {
			toggle(id);
		});
	}
</script>

</html>