Function resolve_self_alignment_safety 

pub(crate) fn resolve_self_alignment_safety(
    alignment: AlignItems,
    overflows: bool,
) -> AlignItemsKeyword

Resolve the safe/unsafe overflow-position fallback for a self-level alignment value (used by align-self / justify-self-style sites and by absolutely-positioned items in flex/grid). If the alignment subject overflows its alignment container and the requested alignment is safe, fall back to logical Start per CSS Box Alignment https://www.w3.org/TR/css-align-3/#overflow-values. Otherwise drop the safety modifier and return the bare keyword.