Technology TLDR: The project uses Node with Express for the server-side, and React on the client-side. Webpack handles building our client-side JS and CSS. Since this project primarily uses ES6 (aka ES2015) Javascript, Webpack uses Babel to transpile the JS so it can be interpreted by the browser.
Building & Running:
To setup up this project, git clone it onto your machine, cd into the project, and then run npm install. Once all of the required modules are downloaded, you'll need to start a server for the project, so just run npm start.
Components: All React components should be placed in the src/components directory.
Static Files: When we build/rebuild our project with Webpack, it produces a file called src/static/js/bundle.js. bundle.js contains our entire React project bundled into one uglified JS file. Our root HTML file, src/static/index.html, imports this file as a script and the uglified React updates the contents of the DOM element with id="main". Our Webpack build process also builds CSS from around the project into a uglified CSS file called src/static/css/styles.css, which is also imported into our root HTML file. There's an additional src/static/base.css file that holds CSS that needs to affect DOM elements that are higher than the scope of React components (like <body> or <html>). Static assets like images, videos, p5.js animations, etc are also in the src/static directory.
The file placement convention we follow is to simply create a CSS file (or several) within the same folder as the component you wish to style. Applying styles to specific elements within those components is as simple as specifying a className in JSX, making it styleable from CSS.