Learn French: La grâce du danseur est de plus en plus impressionnante. - The dancer's grace is more and more impressive.

It translates to 'more and more' and is used to show a progressive increase. Just like in English, you place it directly before the adjective it modifies, which in this case is impressionnante.

How do I pronounce the 's' in de plus en plus?

You must make a liaison between the first plus and en, creating a 'Z' sound (de plu-Z-en plus). Because the next word impressionnante also starts with a vowel, you will often hear a second liaison connecting them as well (plu-Z-impressionnante).

Since danseur is a masculine word, why does the adjective impressionnante have a feminine 'e' at the end?

The adjective is describing la grâce (the grace), which is a feminine noun, not the dancer himself. In French, adjectives must always agree in gender with the core noun they describe.

Why do we say du danseur instead of de le danseur?

In French, whenever the preposition de (of) is followed by the masculine word le (the), they must combine into the single word du. You will never see de le written together.