Tangram
Drag the seven coloured pieces into the grey silhouette, tap to turn them 45 degrees and flip the parallelogram over; fill it and the shape turns vermilion. Eight shapes in all.
Built with
How it was made
Written with Claude Code as a single web page with no libraries; a piece counts as placed by comparing its rotated, flipped corners with the slot's, so a square turned 90 degrees or two identical triangles swapped still fit.