Advanced CSS Variables

Advanced CSS Variables — Dynamic CSS custom properties with JavaScript, scoping strategies, and theme systems. The guide walks through Dynamic Variables. Read: `getComputedStyle(el).getPropertyValue("--var")`. Set: `el.style.setProperty("--var", value)`. Use for: theme toggling (dark/light), mouse position tracking (`--mouse-x`), responsive layouts. Media queries can change variable values. Combine with calc() for dynamic sizing. Animation: transition variable changes. The guide is organized into 1 sections that build on each other, each pairing a prose explanation with real CSS you can use as-is. Related guides: CSS Introduction, CSS Selectors, CSS Box Model, CSS Flexbox, CSS Grid. This is one of 68 CSS guides on CSS Reference — see the full list on the guides page. Look up any property mentioned in this guide from the search page or the CSS Reference homepage.