I downloaded mvasilkov/systematize latest release and tried to input npm install —save systematize in terminal but got this:⸨░░░░░░░░░░░░░░░░░░⸩ ⠇ rollbackFailedOptional: verb npm-session 5b64df302bdd24b
) and font didn’t change to SF when I open websites on safari.
So I wonder is there any following steps I can take.
Looks like what you've send is scss alternative for normalize.css (https://github.com/necolas/normalize.css) and if you're familiar HTML and CSS and don't want to get in touch with NPM you could use css version and just include this file: https://necolas.github.io/normalize.css/latest/normalize.css in your code. This should add all the rules you need and behave as expected.