sibling-count() and sibling-index()The sibling-count() and sibling-index() CSS functions return integers that are useful to style elements based on their positions among siblings or on the number of siblings, for example as part of a calc() expression.cssCSSnewly2026-08-18https://drafts.csswg.org/css-values-5/#tree-countinghttps://developer.mozilla.org/docs/Web/CSS/Reference/Values/sibling-countcss.types.sibling-countcss.types.sibling-indexhttps://nowyoucanuse.com/features--sibling-count.html