This is the 613th most frequent French word.
extrêmement
Extremely.
In this sentence, 'extrêmement' is used as an adverb of degree to emphasize the attribute of kindness.
Elle est extrêmement gentille.
She is extremely kind.
In this instance, 'extrêmement' is modifying the adverb 'dur' to stress the intensity of their efforts.
Ils ont travaillé extrêmement dur pour réussir.
They worked extremely hard to succeed.
Here, 'extrêmement' intensifies the adjective 'captivant' to convey a strong impression of the movie's appeal.