Support for Tailwinds CSS class names

[ryanbalsdon]

Tailwinds CSS uses some class naming schemes that are not supported in the FromStr implementation. The examples I found when poking around are:

• Negative values (<div class="absolute h-14 w-14 -left-4 -top-4 ..."></div>)
• Arbitrary values (<div class="top-[3px]">)
• Breakpoints (<div class="top-4 md:top-6">)

Looks like the FromStr implementation just needs to support leading-negatives then colons and square brackets in the middle.

[ryanbalsdon]

I found another one! Percentage widths (<div class="w-1/2 ... ">w-1/2</div>) can use a slash character.

Also, I patched the FromStr implementation to allow these characters and everything is working perfectly for me. If there isn't a specific reason to lock the allowed characters down so tightly, I don't mind putting together a PR.

[manyinsects]

I don't think there is, so feel free to open a PR!