98.css – design system for building faithful recreations of Windows 98 UIs

Would be cool if it came with JS to resize, move close windows etc.

Only if it's easy to swap out for your own. It's unlikely the JS it would come from would fit into they way you do things normally (in your project or even your head).

When I was trying to do something similar I left all that stuff to the side on the assumption someone had made a neat wrapper to handle it

...and they did! https://github.com/bokuweb/react-rnd