rsnext/errors/css-global.md

Global CSS Must Be in Your Custom <App>

Why This Error Occurred

An attempt to import Global CSS from a file other than pages/_app.js was made.

Global CSS cannot be used in files other than your Custom <App> due to its side-effects and ordering problems.

Possible Ways to Fix It

Relocate all Global CSS imports to your pages/_app.js file.

Or, update your component to use local CSS (Component-Level CSS) via CSS Modules. This is the preferred approach.

Example

// pages/_app.js
import '../styles.css'

export default function MyApp({ Component, pageProps }) {
  return <Component {...pageProps} />
}