[Solved]-Adding custom styles to the react-styleguidist library-Reactjs

Based on the suggestion of @ArtemSapegin, I found this repository, which turned out to be very helpful! I hope that it will solve someone else problem in the future!

This is how looks my styleguide.config.js.

module.exports = {
    template: {
        head: {
            links: [
                {
                    rel: 'stylesheet',
                    href: 'https://fonts.googleapis.com/css?family=Montserrat:400,600'
                }
            ]
        }
    },
    theme: {
        fontFamily: {
            base: '"Montserrat", sans-serif',
            fontSize: '62.5%'
        }
    }
};