SPFx Webpart - not picking up any styles

I've just upgraded to the latest version of SPFx and when I build a project using yo it all works as expected (no errors), except it doesn't apply any of the styles. I've tried creating multiple projects, and across two different computers, and still the same issue.

I've also tried in the workbench and deploying the solution (package).

Is anyone else seeing this issue, or anything I need to do? Note that I'm using REACT framework option in the yo setup.