[eurasiantiger]

SCSS wins for maintainability.

You could import your favourite design framework (say, bootstrap) as SCSS, change its variables to suit your design, and create any custom components using @extend:

    .custom-component {
      @extend .some-bootstrap-class
    }

Also nothing prevents you from creating mixins, functions, etc.

Just keep it first-order, as SCSS functions cannot return new functions.

[jeffhuys]

In tailwind, it's in the tailwind config. Same stuff, basically.