CSS custom property (variable) generation for LiveStyle.

This module handles generating CSS output for:

• @property rules (for typed CSS variables)
• CSS custom property declarations in :root

@property Rules

Typed variables get @property rules for animation support:

@property --color { syntax: "<color>"; inherits: true; initial-value: blue }

CSS Variable Rules

Variables are grouped by their at-rule conditions:

:root{--v12345:blue;--v67890:red;}
@media (prefers-color-scheme: dark){:root{--v12345:lightblue;}}

StyleX Compatibility

Output follows StyleX's minified format:

• No spaces around colons or semicolons
• No newlines between declarations