These are free and open-source themes used for ArtCat Hosting artist and art gallery websites.
They use the Liquid templating language.
Any non-template assets needed, such as CSS or Javascript files, should be put in the assets directory, and a file with a list of the asset file names called files.txt (one file per line) should be put in that same directory. CSS files will be loaded into the template, in the order specified in files.txt, using the tag {% client_css %}. Similarly, Javascript files will be put into the template where the tag {% client_js %} appears.
Modernizr and jQuery are already available without adding those. See this file for an example:
https://github.com/bhoggard/artcat-templates/blob/master/artist/aurora/layouts/application.liquid