Programming Concept.

A clean modern knowledge card explaining recursion in programming. A central illustration shows nested Russian dolls opening one inside another as a visual metaphor. Beside the dolls, a code snippet in a dark-themed editor demonstrates a factorial function. Colorful arrows trace the call stack flowing downward then returning upward. The card uses a dark charcoal background with syntax-highlighted accents in teal, magenta, and gold. A concise definition in white text sits at the top.