Sass variables and CSS Custom Properties (a.k.a. CSS variables) are pretty different from each other [1].

If you want to use CSS Nesting and be backwards compatible with older browsers, the PostCSS plugin postcss-preset-env handles that and lots of other new CSS features that older browsers don't support [2].

[1]: https://sass-lang.com/blog/sass-and-native-nesting/

[2]: https://preset-env.cssdb.org