bug: handling classnames with hyphens properly

[gursuj]

1. A class that uses css variables as arbitrary values like bg-[--my-color] has the following css: background: var(--my-color);. Tailwind docs
   But the converter converts it to background: --my-color;

2. Prefixing classnames with numeric values uses their negative values. e.g: -z-50 should translate to z-index: -50 but isn't converted at all