Sunborn Rising: Beneath the Fall by Aaron Safronoff

Cerulean.

A distant world of Great Trees floating on an ocean surrounding a star.

The flotilla forests cycle light and water through their boughs into their lush canopies. But the once vibrant treescape has grown dark, slowly, subtly over many generations. The civilization of creatures living among the boughs believe the darkness is normal. That is, until one willful young girl named Barra discovers the hidden journal of her late father.

Poring over her father's writing, Barra learns of a mysterious plague, a creeping vine choking the flow of light and water into the canopy. Her father warned the Elders. He urged them to take action. Those were his last words.

Together with her two best friends, a Rugosic named Tory and a Kolalabat named Plicks, Barra will explore every bark, wood, and leaf of the Great Forest to relight her world and complete her father's story, even if it leads her beneath the Fall.