The event was a colossal failure
To italicize something means to emphasize certain words or parts of a sentence or paragraph.
Italicize it.
You underline or italicize them.
You don't, you italicize them.
You wouldn't italicize the entire phrase, no..You would italicize "New York Times" but not Bestseller.For example: "...in the New York Times Bestseller by..."
It would look nicer to italicize The Federalist Papers, but it is also acceptable to underline the title of books.
Your answer depends on your use in a context of the word opera.
ITALICIZE
How would you use theory in a sentence
Either underline or italicize.
You would underline or italicize the name of the book on tape rather than use quotation marks.
Consult the style guide for the publication you're writing for, but it's common to either italicize or underline book titles.(This is not something magic about The Hunger Gamesspecifically; you should do it for any book. For other types of publications ... again, consult the style guide.)