Why Your Next.js Styles Break in Production (And How to Fix It) - By Sourav Mishra (@souravvmishra)
CSS working locally but broken in prod? I explain why this happens in Next.js, from hydration mismatches to CSS order wars, and how to solve it.
It’s the classic "works on my machine" nightmare. You build a beautiful UI with Tailwind and Shadcn, everything looks perfect on localhost:3000. You deploy to Vercel, and suddenly:
- Buttons are the wrong color.
- Layouts shift uncontrollably.
- Fonts flicker.
In this guide, I, Sourav Mishra, Co-founder of Codestam Technologies, break down why Next.js styles often break in production and the exact debugging protocol we use at Codestam.
The Root Cause: Order Matters
In development, Next.js injects styles on demand as you navigate. In production, CSS is bundled into chunks. If your import order is inconsistent, the "winning" style might change.
The "Global CSS" Trap
The most common culprit is importing globals.css in the wrong place.
❌ BAD: Importing it in a random component.
// app/dashboard/page.tsx
import '../globals.css'; // Don't do this!
✅ GOOD: Import it once in the root layout, at the very top.
// app/layout.tsx
import './globals.css'; // Top of the file
import { Inter } from 'next/font/google';
Tailwind vs. Shadcn Conflicts
If you use Shadcn UI (which uses Tailwind), you might face specificity wars. One common issue is the !important flag or class merging collisions.
Solution: tailwind-merge
Always use a utility like cn() (standard in Shadcn) to merge classes safely.
import { clsx, type ClassValue } from "clsx"
import { twMerge } from "tailwind-merge"
export function cn(...inputs: ClassValue[]) {
return twMerge(clsx(inputs))
}
Why cn() Matters
We once spent 3 days debugging a "broken" button at Codestam Technologies only to realize that bg-red-500 was being overwritten by a default bg-blue-500 because of class ordering in the bundled CSS. tailwind-merge solves this by deterministically resolving conflicts based on Tailwind's own configuration.
Hydration Mismatches (The Flicker)
If your toggle theme (Dark/Light) flashes on load, it's a hydration mismatch. The server renders "Light" but the client has "Dark" in local storage.
Fix: Use next-themes with the suppressHydrationWarning prop.
<html lang="en" suppressHydrationWarning>
<body>
<ThemeProvider attribute="class">
{children}
</ThemeProvider>
</body>
</html>
The "Build-While-Dev" Conflict
A classic "gotcha" that breaks styles locally: Running next build while next dev is active.
Both processes fight over the .next folder. This often results in a corrupted cache where styles look broken even after you refresh.
The Fix:
- Stop the dev server (
Ctrl + C). - Run the build.
- Restart the dev server.
[!NOTE] In Next.js 16, this is largely mitigated if you use Turbopack (
next dev --turbo), as it handles file locking better than Webpack.
Debugging Checklist
- Delete
.nextfolder: Runrm -rf .nextand build locally (npm run build && npm start) to reproduce the error. - Check Third-Party CSS: Are you importing a carousel or datepicker's CSS in a client component? Move it to
layout.tsxor a dedicated client wrapper. - Inspect the Build Output: Look for "Conflicting Order" warnings in your terminal during build.
Conclusion
Production CSS issues are almost always due to import order or specificity conflicts. By adhering to a strict import hierarchy and using tools like tailwind-merge, you can sleep soundly.
For more Next.js tips, check out my guide on Mastering Cache Components.
This guide was written by Sourav Mishra, Co-founder of Codestam Technologies and a Full Stack Engineer.