CSSOM

RU: CSSOM

CSS Object Model: a browser API that represents parsed stylesheets and computed styles as JavaScript objects, analogous to the DOM for HTML. Scripts read and modify rules via interfaces such as CSSStyleSheet and CSSStyleDeclaration; every CSSOM mutation triggers a style-cascade rebuild, but layout (reflow) is only triggered when the changed properties affect element geometry or position — paint-only changes such as color or background-color cause a repaint instead.