How to prevent .dark mode classes being purged in angular 19 app when deploying to production

[MIJohnson]

I'm using tailwind 4 with angular 19 app. everything works great on dev, but I don't seem to be able to find a way to prevent all .dark css classes being purged as soon as I build for production. given that tailwind.config.js config approaches is no longer an option AFAIK what is the way to do this now? I have also tried adding @layer without any luck i.e

@layer base {
  .dark\:border-teal-600 {
    border-color: var(--color-teal-600);
  }
}

i have installed everything as per https://tailwindcss.com/docs/installation/framework-guides/angular