System.css is a CSS library for building interfaces that resemble Apple's System OS which ran from 1984-1991. Design-wise, not much really changed from System 1 to System 6; however this library is based on System 6 as it was the final monochrome version of MacOS.
Fortunately, this library does not use any JavaScript and is compatible with any front-end framework of your choice. Most styles can also be overwritten to allow for deeper customization.
This is a paragraph! Here's how you make a link: Neocities.
Here's how you can make bold and italic text.
Here's how you can add an image:
Here's how to make a list:
To learn more HTML/CSS, check out these tutorials!