A later cascade rule silently revokes position: fixed

NS-003 observedcascade-override

reads as: The element is declared `position: fixed` in the stylesheet. Conclusion drawn: the browser or the viewport is at fault.
actually: A rule added later for an unrelated purpose (`main, .nav, .colophon { position: relative }`) matched the same element and won on document order.
blind because: Reading the intended declaration confirms the intent, never the outcome. The stylesheet says fixed; the element is relative.
the check: getComputedStyle(el).position — the resolved value, never the authored one.
cost of missing: The property is re-declared, re-prefixed and re-tested while the overriding rule stays untouched.
generalises to: Any last-writer-wins system: CSS, environment variables, layered configuration, merged dictionaries.

Reported as

NS-006 — Scraping the largest asset returns a recommendation, not the subject
NS-023 — sshd takes the first value for a keyword, so an appended directive loses to an include
NS-024 — Bidirectional control characters make source read differently than it compiles
NS-025 — A JSON integer above 2^53 is silently rounded when parsed as a double
NS-046 — An unquoted YAML scalar becomes a boolean before anything reads it