Create an event poster for [Event Name]. Arrange three overlapping cool-white flyers emerging from an open [Envelope Color] paper envelope, with visible triangular folds. Repeat a large, heavy condensed black event headline and a hand-drawn illustration of [Activity] on all three flyers. Use a vivid [Background Color] background. Add an irregular black masthead directly on the background, four theme-specific cutout stickers with white borders, and small date and venue details. Keep the paper texture subtle, the whites clean, and the colors saturated. Keep the envelope-and-flyer structure fixed. Change the event, palette, illustration, and stickers.