The website is jekyll-based (which you know plenty about!). The resume page at mapsam.com/resume uses these key files:

1. _layouts/resume.html: this is template for the resume page. You'll notice a few different for loops on this page that look for jobs, cv items, and extras formally declared as "things" because I couldn't come up with a better word 😄
2. resume/index.md: this is the meat of the potato, where all of the "data" for the resume exist. Notice in the YAML (the syntax for the top part of the file between the --- triple dashes) there are sections for jobs, cv, and extras. This file also inclues layout: resume at the top, which grabs the file in item #1 above and uses those loops. This file is called index.md and is located within /resume directory so you can go to mapsam.com/resume without having to provide a specific file (i.e. mapsam.com/resume.html). Index.md is grabbed by jekyll, uses the specified layout, and generates an HTML file called index.html (which you can't see). Web systems (like github pages) default to generating the index.html file when they load a URL that points to a directory. Note: I linked to the "raw" file above because GitHub tries to render this .md in a weird way, which makes reading the YAML difficult.
3. css/mapsam.css: the styles for the resume are found on these lines. They tie in with the class names defined in the HTML of the resume layout in #1.