Ionic PWA Toolkit - override sass varibles

Hi, I have a question regarding the Ionic PWA Toolkit based on Stencil and Ionic4.
I want to override the Ionic default theme in one of my components. In a Ionic project you should do it like this: https://ionicframework.com/docs/theming/theming-your-app/
How can I do the same with Ionic PWA Toolkit?