Title: Starry Letter
Prompt: Create a responsive offline nighttime letter page with a CSS envelope, dark blue background, refined serif typography and a button that opens the envelope and reveals a message. Inline all code.
Description: An imaginary letter from the night offers a small note of light.
Visual techniques: clipped envelope flap, warm paper colors, dark atmospheric background, smooth transition.
Interaction model: A button opens or closes the envelope and changes the message.