WPT details: https://wpt.fyi/css/css-contain/container-queries/container-selection-unknown-features.html https://wpt.fyi/css/css-contain/container-queries/query-evaluation.html https://wpt.fyi/css/css-contain/container-queries/query-evaluation-style.html
@container selectors that contain unsupported queries will never select any containers, meaning they will never match. That means this query will never match any container even if there is a size container that will match the width query that would otherwise make the selector match in cases like this: @container (width > 0px) or (unknown) {} This is a recent change to the specification to avoid forward-compatibility issues.
Spec changed for better forward compat. Want to ship change before counter increases: https://chromestatus.com/metrics/feature/timeline/popularity/4596