Four short lines, and the poem keeps repeating the same shape: "the littlest things are..." and then a new description each time. What changes is the word at the end of each line, and that is where the feeling lives.
The speaker starts with "stupidest," which sounds almost dismissive, as if small things are silly and not worth the attention. Then comes "craziest," which feels a bit more affectionate, even amused. By the last line, the tone turns completely: the littlest things are "the most beautiful." The poem moves from mocking to marveling in just a few words.
That shift is the whole point. The speaker seems to be saying that tiny details can be silly, strange, and wonderful all at once, and that these descriptions don't cancel each other out. The poem doesn't say which small things it means, so readers can fill in their own, perhaps a private joke or an odd habit. The mood is light, playful, and quietly tender.