Both Uses

theme
in
The Selection, by Kiera Cass
(Edited)

Slowly, others started to trickle in. I quickly noticed a theme. Every one of the girls looked phenomenal. They had their hair pulled up in intricate braids or curls, away from their faces. The makeup was meticulously done, dresses pressed to perfection.
p. 121.8

theme = recurring idea
Sure enough, the room was full of dresses in every shade of blue. Some of them fell closer to green, others closer to purple, but it was clear there was a theme.
p. 237.7 *

theme = repeated idea

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)