CSS-in-JS Styles Not Applying in Build

1. Library not configured in vite.config.js
2. Babel plugin missing for CSS extraction
3. Build step doesn't extract critical CSS
4. SSR mismatch between server and client rendering
5. Class name generation not deterministic

Configure styled-components in vite.config.js:

import { defineConfig } from 'vite';

export default defineConfig({
  plugins: [
    react({
      babel: {
        plugins: [
          ['babel-plugin-styled-components']
        ]
      }
    })
  ]
})

Or switch to Tailwind for simpler CSS setup.