You're more than welcome to copy the code directly into your project (https://unpkg.com/css-media-vars@1.0.1/css-media-vars.css) or read the code, learn the technique, and implement it yourself. NPM is just one option for how to use the author's flavor of the technique.
Comments
When I clicked to see vanilla CSS, an NPM package was not something I expected to see.
You're more than welcome to copy the code directly into your project (https://unpkg.com/css-media-vars@1.0.1/css-media-vars.css) or read the code, learn the technique, and implement it yourself. NPM is just one option for how to use the author's flavor of the technique.
Seems like it's just being used as a distribution method here.