Variables are a basic tool that help organize colors on a project. For a long time, front-end engineers used preprocessor variables to configure colors on a project. But now, many developers prefer the modern native mechanism for organizing color variables: CSS Custom Properties. Their most important advantage over preprocessor variables is that they work in realtime, not at the compilation stage of the project, and have support for the cascade model which allows you to use inheritance and redefinition of values on the fly.

https://www.smashingmagazine.com/2020/08/application-color-schemes-css-custom-properties/