Provided is a display device or an input/output device in which reflection of outside light is reduced. The display device includes a first substrate and a second substrate. The first substrate includes a first surface. A transistor is over the first surface. The second substrate includes a second surface. A first structure having a projection, a second structure having a projection, a black matrix covering the first structure and the second structure, and a color filter are over the second surface. The first surface faces the second surface. The black matrix has a plurality of projections reflecting the projection of the first structure and the projection of the second structure. A planar shape of the first structure is different from a planar shape of the second structure.