The great thing about styled-components is that you don't need to rewire anything to work with third party component libraries. Example:

import styled from 'styled-components';
import { RaisedButton } from 'material-ui';

const StyledButton = styled(RaisedButton)`
  > button {
    background: papayawhip !important;
    color: palevioletred !important;
    padding: 0 0.75em !important;
  }
`;

(live demo)

What styled-components does under the hood is pass in a className to the RaisedButton. As long as that className is attached to a DOM node somewhere inside the RaisedButton it works perfectly! 🎉 (see the styled-components docs)

Specifically material-ui is a bit of a pain because it uses inline styles and has lots of wrapper divs, but nothing a !important and some nesting here and there can't remedy.