Box Shadow Syntax
The CSS box-shadow property accepts values in the format: offset-x offset-y blur-radius spread-radius color. Optional inset keyword places the shadow inside the element. Multiple shadows are separated by commas and rendered in stack order, with the first shadow on top.
Creating Realistic Depth
Realistic shadow effects use multiple layers with different blur and opacity values. A tight shadow with low blur provides definition, while a larger diffused shadow creates ambient occlusion. Combining two or three shadow layers produces natural-looking elevation that mimics real-world lighting conditions.
Performance Considerations
Box shadows are GPU-accelerated in modern browsers but can impact rendering performance when applied to many elements simultaneously. Avoid animating box-shadow directly; instead, use opacity transitions on a pseudo-element with the shadow pre-applied. This technique keeps animations smooth at 60fps.
Browser Compatibility
CSS box-shadow is supported in all modern browsers including Chrome, Firefox, Safari, and Edge. No vendor prefixes are needed. For very old browsers, consider providing a solid border as a fallback. The inset keyword and multiple shadow support are universally available.
