Is it a violation of the Due Process Clause and defendant's Sixth Amendment right to require the State to prove a criminal charge beyond a reasonable doubt to a jury when a reviewing court decides his case by weighing the credibility of the witnesses?

QUESTION PRESENTED A jury convicted petitioner of unlawful possession of ammunition, which police found in a cardboard box in the trunk of his car. Petitioner testified he did not know it was there. The trial court refused a mistake-of-fact jury instruction that would have told the jury a defendant is not guilty of unlawful possession if he did not have the required mental state because he did not know a fact. The California Court of Appeal ruled that any error was harmless because petitioner’s testimony that he was unaware of the ammunition “did not overcome” what the appellate court called the “extremely strong evidence” presented by the testimony of the State’s witnesses. Is it a violation of the Due Process Clause and defendant's Sixth Amendment right to require the State to prove a criminal charge beyond a reasonable doubt to a jury when a reviewing court decides his case by weighing the credibility of the witnesses? i