Does Ant Design come with its own stylesheets? If they're using any preprocessor it might be good to stick with what your tools are already using.
I definitely see a lot more use of preprocessors than I do benefit from them, but since you are using React I'd say - if you want to experiment with a 'new way' of styling things, and you already are using React -> look into Styled Components and Glamorous for a 'CSS-in-JS' workflow that you can really only do on websites where you have a JS framework like React putting together your HTML.
At the end of the day, most projects can still get by just fine with a CSS stylesheet written as CSS, so make sure whatever abstraction you pick for writing your CSS doesn't make it more difficult than that (it's not as hard as the makers of some of these tools would have you believe!)