The sass installation document is directing to this link

[Manimestro]

Adding a Sass Stylesheet Note: this feature is available with react-scripts@2.0.0 and higher.

Generally, we recommend that you don’t reuse the same CSS classes across different components. For example, instead of using a .Button CSS class in and components, we recommend creating a component with its own .Button styles, that both and can render (but not inherit).