Old post but still relevant, so adding an answer to help those with similar issue
While not inherently possible in CSS modules alone, the author of the react-toolbox library has actually solved this particular problem very nicely
Read their github docs which are more in depth on the subject at https://github.com/react-toolbox/react-toolbox#customizing-components
A list of the themeable classes for a particular component is given on the component demo page on their site too
In your case as well as passing a className for tab, you would also create a theme with classes that overrides that desired parts of the default theme and pass that as the theme prop. For example something alog the lines of…
MyComponentWithTabs.css
.tab {
color: white;
}
MyTabTheme.css
.active {
color: hotpink;
}
MyComponentWithTabs.js
import styles from './MyComponentWithTabs.css'
import tabTheme from './MyTabTheme.css'
// blah blah...
return <Tab key={index} className={styles.tab} theme={tabTheme} />
Under the surface this uses a decorator they have abstracted into separate library react-css-themr, I recommend giving that a read too as it explains how the defaults are composed with your overrides in much greater depth, including the different merging strategies they use