All 3 Uses

theme
in
Flags of Our Fathers
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Floats with agricultural themes would follow the high-school band as it marched down the paved main streets.†
Chpt 2. *
As the Treasury Department shaped its theme for the "Mighty 7th," it enjoyed the wholehearted support of Madison Avenue.†
Chpt 15.
Again and again, despite abundant opportunity, the three boys refused to pick up the theme of press and speechmakers and portray themselves as valiant warriors who hoisted the colors against sheets of enemy fire.†
Chpt 16.

Definitions:

(1) (theme as in: theme of the novel)
a basic idea that underlies what is being said or done -- especially in a literary or artistic work
(2) (theme as in: musical theme)
the initial or primary melody of a musical composition

or

(as in "theme song") music that is most repeated in a film, television series, or other theatrical production
(3) (theme as in: wrote a 2-page theme on my summer)
an essay written by a student

(This sense of theme is much rarer in recent decades than in the past.)
(4) (meaning too rare to warrant focus)