What is 'You are stunning' when translated from English to Italian?

Sei bellissimo! and Sei molto bello! are Italian equivalents of the English phrase "You are very handsome!"

Specifically, the present indicative verb sei is "(informal singular you) are". The masculine superlative bellissimo means "extremely/very handsome, handsomest". The adverb molto means "very". The masculine adjective bello translates as "handsome" in this context.

The respective pronunciations will be "seh-ee bel-LEES-see-mo" and "seh-ee MOL-to BEL-lo" in Italian.