Design a cozy night-themed image featuring: 1. A dark navy background with a gradient transitioning to lighter hues toward the top. 2. A large, simple white envelope at the center, slightly opened to suggest a welcoming feel. 3. A crescent moon with a soft glow in one corner and scattered whimsical stars around the envelope. 4. Replace the sack with a basket made from natural materials, overflowing with colorful, hand-drawn letters and postcards. 5. Use a variety of bold and pastel colors for the envelopes, but ensure none contain recognizable brand logos. 6. Add a soft shadow under the basket for depth, and keep the overall tone warm and inviting.