"It is a clear night."
Translation:Es una noche clara.
yes, it is. We use 'claro' for ideas that now you know better. For example your two sentences, ahora todo está más claro, ella ha dejado las reglas claras, etc.
Furthermore, 'claro' is uses too for 'more light color'. For example: si pones más blanco el color será más claro (if you put more white in the picture then the color is lighter).
Maybe 'claro' has other uses in Spanish...
Duo's emphasis on ser=permanent and estar=temporary does NOT reflect a hard and fast rule by any means. Being dead uses estar, not ser, and death is about as permanent a condition as there is! ;)
I think a Google search for "ser and estar" and a little off-Duo study will really help all the folks here that are having problems. Weather, in general, is a different kettle of fish in Spanish and worthy of another Google, IMO.