Sorry, but you either have no stories or none are selected somehow.
If the problem persists, check the browser console, or the terminal you've run Storybook from.
Our design system accepts theming via scss variables. To change a theme for a component, you'll just need to override the corresponding theme variable.
To do that, take a look at which are the default themes in our _settings.scss file, and which themes are available for the components in the _colors.scss file.
To change the themes, you may need to import our variables files before overwriting. To properly overwrite the Button theme, for example, you may need to do something like this: