Function reapply_detached 

pub fn reapply_detached(
    el: &mut Element,
    css: &Stylesheet,
    media: &MediaContext,
)

Resolve a detached element (one with no ancestors to hand it a scope, such as a <for> row being built before it joins the tree) against the stylesheet, and write what the cascade resolved over its attributes.

The element’s own declarations (Attributes::markup_styles) rank above every rule, as they did in the first cascade. Every --* property any rule declares seeds the scope, first value wins, so a var() still resolves against globals the missing ancestors would have carried. A property no rule and no declaration sets keeps the value el already had: the element’s place in the tree decides the rest, and the restyle that runs once it is in place resolves it whole.