Learn Italian: Ieri ha comprato diversi ombretti. - She bought several eyeshadows yesterday.

The meaning of diverso changes based on its position. When it comes before the noun (as in diversi ombretti), it acts as an indefinite adjective meaning "several" or "various." If it were placed after the noun (like ombretti diversi), it would mean "different eyeshadows."

Could I use parecchi or vari instead of diversi in this sentence?

Yes! In this context, parecchi (quite a few or several) or vari (various or several) would mean practically the same thing. You could say ha comprato parecchi ombretti or ha comprato vari ombretti and the meaning would remain the same.

Why is the masculine plural form diversi used here?

Indefinite adjectives must agree in gender and number with the noun they describe. The word for eyeshadow, ombretto, is a masculine noun. Since she bought more than one, we use the masculine plural ombretti, which requires the masculine plural adjective diversi.

The translation says "She bought," but couldn't ha comprato also mean "He bought"?

Absolutely. In Italian, the subject pronoun (lui or lei) is usually dropped because the verb form gives enough context in a real conversation. Without a wider story, ha comprato could mean "he bought," "she bought," or even the formal "you bought." The translation simply provides "She" as one likely interpretation!