are they included in your tailwind config? and are you importing your tailwind config?

In shadcn I copied the layout.tsx file directly and there was no globals.css

well you need to have the styles file for tailwind...

If you used create-next-app and used tailwind
all you have to do is open the terminal and run npx shadcn-ui@latest init

and if you wanna add components use
npx shadcn-ui@latest add button or any other element like npx shadcn-ui@latest add dialog

in top of your page.tsx or wherever you wanna display your components use:
import { Button } from "@/components/ui/button" or similar. You can see on each shadcn component page how to use that component.

Here's the guide for installing shadcn ui library: https://ui.shadcn.com/docs/installation/next