Function parse_border_shorthand 

pub fn parse_border_shorthand(
    ctx: &str,
    name: &str,
    value: &str,
) -> Result<BorderShorthand, ParseError>

CSS border shorthand: <width> || <style> || <color> in any order (e.g. 1px solid #444). border: none clears the border.

Lenient extension: when the style keyword is omitted but a width or color is present (border: 1px #444), the style resolves to solid; the IR stores the normalized form, so a transpile target emits the explicit 1px solid #444 and renders identically in a real browser.