Purim 2025: What is the source in the Megilah for the opposing opinions of רשב"י and his talmidim ?

Where did they get the ideas that the big sin of כְּלַל יִשְׂרָאֵל was either a.) נֶהֱנוּ מִסְּעֻדָּתוֹ שֶׁל אֲחַשְׁוֵרוֹשׁ or b.) הִשְׁתַּחֲווּ לַצֶּלֶם? It is not in the text of the Megilah, is it?