CSS Box Model, Cascade, and Specificity Explained for Web Developers

Every HTML element is rendered as a rectangular box consisting of four layers: content, padding, border, and margin. The box-sizing property determines whether declared widths apply only to content (content-box) or include padding and border (border-box), with border-box being the preferred choice among most developers. When multiple CSS rules target the same element, the browser resolves conflicts through the cascade, which weighs origin, specificity, and source order. Specificity is a scoring system where inline styles outrank ID selectors, which outrank class selectors, which in turn outrank element selectors. While !important can override the cascade, overusing it makes stylesheets harder to maintain and debug.