These two sentences share the same case relationship.
لَا رَجُلٌ صَالِحًا
- رَجُلٌ is the marfu ism of لَا.
- صَالِحًا is its mansub khabar.
لَيْسَ زَيْدٌ طَوِيلًا
- زَيْدٌ is the marfu ism of لَيْسَ.
- طَوِيلًا is its mansub khabar.
In both examples, the second descriptive noun is the mansub element.