How do I set a default theme?

I'm building a product based on the Intellij platform. In this product, I would like to set a certain sub-theme from the material theme for intellij, as the default theme for the application. I would like the theme to be set before the customize ide steps dialog on first run, so that even these steps are shown in the desired theme.

What would be the simplest way to do this? Any direction would be greatly appreciated.

Thanks,
Alex