Use libraries that come in Sass form or figure out how you use them in a Sass-y way. In your Sass file (style.scss), write .nav { @extend .lib-nav-thing } and c

Use libraries that come in Sass form or figure out how you use them in a Sass-y way. In your Sass file (style.scss), write .nav { @extend .lib-nav-thing } and compile a new style.css. You won't have to touch your HTML.