Learn Portuguese (Portugal): Esta caixa está vazia, não esconde nada. - This box is empty, it doesn't hide anything.

In Portuguese, double negatives don't cancel each other out like they do in English. When a negative word like nada (nothing/anything) comes after the verb, you must put não (not) before the verb. So, não esconde nada is the standard, grammatically correct way to say "it doesn't hide anything."

Why use está for "is" here instead of é?

You use está (from the verb estar) because being empty (vazia) is a temporary state or condition. The box is empty right now, but it could be filled later. If you were describing a permanent characteristic, like what the box is made of, you would use é (from the verb ser).

Why is the word for empty vazia instead of vazio?

Adjectives in Portuguese have to match the gender of the noun they describe. Because caixa (box) is a feminine word, the adjective takes its feminine form, vazia.

Where is the word for "it" in the second half of the sentence?

Portuguese frequently drops subject pronouns (like "he", "she", or "it") when it is obvious who or what is doing the action. The verb esconde (hides) is already conjugated for the "he/she/it" form, and we know from the first half of the sentence that it refers back to the box.