Yeah, Tailwind uses postcss to let you use its utility classes with the normal way of doing abstractions in CSS - but it also promotes using Javascript component frameworks where that makes sense.

The utility classes are in themselves great. It's a complete set but it still promotes thinking in design systems.

CSS classes are good, but should be used in moderation. Since you're likely using a component framework anyway, you can often just use the utility classes directly in your components with no loss of clarity and without repeating yourself. But when you do end up repeating yourself in the CSS, you can reach for postcss's @apply and have access to Tailwind's design system. The three levels work extremely well together.