fix: compare css contents correctly before writing file

[a16n-dev]

I noticed the buildCSS function seems to be doing an incorrect comparison:

// This is a file path
const cssFile = path.join(dirname, '../../uniwind.css')

// This is file contents
const oldCSSFile = fs.existsSync(cssFile)
  ? fs.readFileSync(cssFile, 'utf-8')
  : ''

// These will never be equal
if (oldCSSFile === cssFile) {
  return
}

[Brentlok]

Nice catch 👌