Design Systems Handbook

It wasn’t hard to get them to follow the guidelines, it was hard to get them to agree on the guidelines.”

a tool like CSS Stats to see how many rules, selectors, declarations, and properties you have in your style sheets.

But in general, what I see most design systems break things down into are:
elements (or basics, or atoms)—these are small, stand-alone components like buttons and icons
components (or molecules, or modules)—these are usually an assembly of small components into a larger component like a search form (which includes a form input, a button, and potentially even a search icon)
regions (or zones, or organisms)—these are an area of the UI like a left-hand navigation
layouts—how the pieces are laid out on the page (like a header region, followed by a sidebar and main content area, followed by a footer)