Example 3: Controlling Stack Order with `z-index`
Using `z-10`, `z-20`, etc., on positioned elements to control overlap.
Parent Container (`relative`)
Layer 1 (z-10)
Layer 2 (z-20)
Layer 3 (no z-index / z-auto)
Note: `z-index` only works on
positioned elements (relative, absolute, etc.).
All layers here are `absolute`.