The old film camera
PencilChallenging

Give a closed envelope subtle depth with angled folds and a narrow paper edge. A heart seal and small gray accents complete the sketch.
Draw a wide rectangle at a gentle angle with slightly softened corners. Add a narrow lower edge to suggest the paper thickness.
Bring the top flap toward the center and add the two lower fold lines. Leave their joins readable instead of adding many creases.
Place a small heart where the flap closes. Add a few short crease marks and a narrow gray accent under the flap and envelope.
A small thing to tryKeep the flap shadow narrow. Its edge can lift away from the envelope without shading the whole paper surface.