What do u mean by default color? The default background color? In your css file "@layer base {" -> ".dark {" -> "--background: 240 10% 3.9%;"

Have you tried to use the ThemeProvider and set the defaultTheme attribute to dark?
https://ui.shadcn.com/docs/dark-mode/next

<ThemeProvider
  attribute="class"
  defaultTheme="system"
  enableSystem
  disableTransitionOnChange
>

Yes the nextjs discord will have the answer and not the shadcn/ui documentation with a whole section on themes

Hi @starload7744 if this solved your problem. please mark as solution.

no it didnt

have you even tried it? where's the problem?