Core Framework

link - developer.microsoft.com/en-us/fabric#/styles
These are the core elements of the design language, including icons, colors, type, and grid.
The Fabric Core project includes all of the base styling that's used throughout Microsoft.

npm install 

Nuget Package - OfficeFabricUICore
NPM Package Name - office-ui-fabric-core

github.com/OfficeDev/office-ui-fabric-core 

Fluent UI React

Fabric Core is primarily meant for non-React applications or static pages.
If you're using Fluent UI React, you may not need Fabric Core.
Most of the styles from Fabric Core are also available via CSS-in-JS styling, which is the recommended styling approach with Fluent UI React.

Latest Version - 2019 October (11.0.0)

href="https://static2.sharepointonline.com/files/fabric/office-ui-fabric-core/11.0.0/css/fabric.min.css" 

Version History - office-ui-fabric-core