Learn Croatian: Inspektor vidi sve. - The inspector sees everything.

When you want to say "everything" as a general concept without pointing to a specific noun, you use the neuter singular pronoun sve. Here, it is the direct object (what the inspector sees), so it is in the accusative case. For neuter words, the nominative and accusative forms are exactly the same.

Does sve change if the inspector is female?

No. The word sve represents the things being seen ("everything"), not the person seeing them. Even if it were a female inspector (inspektorica), the objects being seen do not change, so the word remains sve.

How would I say "The inspector sees nothing" instead?

You would say Inspektor ne vidi ništa. Remember that when replacing "everything" (sve) with "nothing" (ništa), Croatian requires a double negative, so you must also add ne before the verb.

The infinitive is vidjeti (to see). Why does the present tense form vidi drop the "je"?

The verb vidjeti belongs to a common group of verbs that end in -jeti in the infinitive but take regular -i endings in the present tense. The -je- is dropped, leaving the root vid-, to which we add the third-person singular ending -i.