Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Magical
The book starts out with Tilja snug in bed in a winter wonderland, but magic soon rears its head in every part of her life. Her mother's knocked out by a unicorn, her sister can talk to trees, and her cranky grandma, Meena, needs her help to persuade a magician to rescue the Valley.
Tilja herself, despite initially not thinking she has any magic, finds powers within herself that she didn't even know existed. More than this, though, a sense of wonder imbues her discoveries—whether it's her awe at the majesty of the Empire and its centuries-old traditions, or how her perceptions of the magicians defy her expectations. For example, when Tilja meets The Ropemaker, he looks like some magical creature:
With sick dread Tilja crouched her way to the entrance, hesitated, crawled out and stood. A white mass of fog filled the valley below them, but the moon was high overhead, paling the stars. The stranger was there, a tall, thin shape in the moonlight. At the top of the neck was a normal human face, eyebrows, eyes, a long nose, smiling mouth, a pointed chin and wisp of a beard, and above that the monstrous bulge she'd seen from the cave. (7.102)
Tilja is constantly surprised by the magic of her land, and so is the reader—which means that not only is this book all about magic, but its tone is pretty magical too.