Madi's "Heart Eyes" is a short, tender compliment addressed directly to someone the speaker admires. The focus is on the other person's eyes, which the speaker sees as deep, full of stories the speaker could never fully understand. Some of those stories seem beyond belief, and the speaker doesn't pretend to know them. That admission of not understanding is what makes the praise feel honest rather than gushing.
The poem turns on the small word "But." Even though the speaker can't grasp what lies behind those eyes, the eyes are still lovely. The last line then shifts from the eyes to the whole person: "You're lovely." It's a quiet, simple move, and it suggests the speaker's affection goes beyond appearance.
The title, "Heart Eyes," points to the emoji-like feeling of being smitten. The mood is warm, gentle and a little shy, with a hint of mystery in the idea that this person has a past or inner life the speaker can only glimpse.