This is a good template for working with a simple Leaflet map, bringing in a geoJSON of point data.
Set up for Dave W. @ Harvard with his test historical Black Boston data.
Popups are not configured to show data values, because the data properties are not formatted for JSON, but you can see how that would happen in the main.js file.
You could also pull in the link to the JSON files with links, instead of having the data stored with the website files.
You can see the sidebar is just a regular HTML div element. You can basically put whatever HTML on top of the map and style it however you want.
Spin it up by using a local server like https://www.npmjs.com/package/http-server
You won't be able to see the data points unless you are viewing it on a local server like this ^^