Default error page affects layout content

### Link to the code that reproduces this issue https://github.com/Netail/repro-next-leaking-default-error-page ### To Reproduce 1. Run `yarn install` 2. Run `yarn dev` 3. Visit `localhost:3000/`, on which you can see our "beautiful" custom body styling 4. Visit a non existing page, e.g. `localhost:3000/oops`. ### Current vs. Expected behavior NextJS applies their error styling to the body, messing with our custom styling. The content in the layout is affected too, while it should only be constrained to the layout's children in our case. ### Provide environment information ```bash Operating System: Platform: win32 Arch: x64 Version: Windows 10 Home Available memory (MB): 32702 Available CPU cores: 8 Binaries: Node: 22.11.0 npm: 10.9.0 Yarn: 1.22.22 pnpm: N/A Relevant Packages: next: 15.2.0 // Latest available version is detected (15.2.0). eslint-config-next: N/A react: 19.0.0 react-dom: 19.0.0 typescript: 5.8.2 Next.js Config: output: N/A ``` ### Which area(s) are affected? (Select all that apply) Error Handling ### Which stage(s) are affected? (Select all that apply) next dev (local), next build (local) ### Additional context _No response_