Update class regex

[5need]

Changes the regex that selects classes in a css file to ignore any leading whitespace.

This is useful for when you have whitespace before a class declaration, like a @layer directive.

Before, using ^(\.[^\s]+)[ ]

// output.css
@layer utilities {
  .visible { // ❌ does not match .visible due to leading whitespace :-(
    visibility: visible;
  }
}

After, using ^\s*(\.[^\s]+)[ ] instead

// output.css
@layer utilities {
  .visible { // ✅ matches!
    visibility: visible;
  }
}

[praveenperera]

Makes sense do you mind adding a few tests, that show this @5need thank you!