Film style refers to techniques used by the filmmaker to convey certain types of messages or meanings within the movie. To All the Boys I've Loved Before has various characteristics which speak to its overall style and the atmosphere the director is trying to create.
The filmmakers create a bright, colorful world, almost as though it is filmed through an Instagram filter. Lara Jean wears colorful outfits, and her bedroom, a very important location in the film, is also vibrant. A theme in the film and in the novel on which it is based is fantasy, so it's no surprise that the filmmakers have worked to create a beautiful, bright atmosphere throughout the movie. The filmmakers are tasked with putting Lara Jean's romantic fantasies into her reality, and they do it seamlessly.
Lara Jean is the central character of the movie, and the story is mainly told through her thoughts and experiences alone. The camera often zooms in to focus on Lara Jean's facial expressions, and she narrates much of the story. This turns Lara Jean into an omnipresent narrator who tells her story from her perspective, connecting her more closely to the audience. If the movie did not have Lara Jean's narration or the constant focus on her expressions, it's possible the audience would not feel as close to Lara Jean.