In Chapter 3 of Katherine Paterson's Bridge to Terabithia, the first time both Jesse and Leslie enter the section of the woods they dub Terabithia, Jesse notes that the woods are dark and frightening, "like being under water," but bravely follows Leslie into the woods anyway. He further notes the "ever-darkening columns of tall pines" and the various types of trees: the dogwoods, the redwoods, the oaks, and the evergreens. He further notes that the "sun flung itself in golden streams through the trees to splash warmly at their feet" (p. 24). In other words, because she's there, he doesn't focus on and isn't frightened by the darkness. Instead, he's able to note the golden sunlight and feel its warmth.
Later, in Chapter 13, after Leslie has died, Jesse finally gets the courage to go back to their stream by himself. He also bravely builds a bridge to the other side using a fallen tree branch and makes his way into the deep part of the woods they call their "castle stronghold" (p. 67). However, this time, now that Leslie is gone, he only notes that it is "dark and damp" but also notes that "there was no evidence there to suggest that the queen had died" (p. 67). He also decides to weave a funeral wreath of flowers for her and lay it in the grove. He further notes a "brilliant" red cardinal cock his head and "stare at the wreath" as if the bird was giving its approval of the wreath (p. 68).
Hence, both when he first enters Terabithia with Leslie and much later when he returns after he death, he notes the darkness of the woods. Yet, he is still able to notice other beauties of nature and feel brave, all due to her influence.