The box-shadow property is one of the most underused tools in CSS. Most developers use it for a single subtle drop shadow and stop there — but the full syntax supports layered shadows, inset effects, and colour-based glows that can replace entire images. This guide covers everything from the basic syntax to advanced multi-layer techniques. The full syntax box-shadow : [ inset ] offset-x offset-y [ blur-radius ] [ spread-radius ] color ; Each part: offset-x — horizontal distance. Positive = right