# Advanced Tree Counting: Mathematical Layouts With \`sibling-index()\` And \`sibling-count()\`

DevFeed: [Advanced Tree Counting: Mathematical Layouts With \`sibling-index()\` And \`sibling-count()\`](<https://devfeed.tech/articles/advanced-tree-counting-mathematical-layouts-with-sibling-index-and-sibling-count-4280.md>)

Original publisher: [Read original article](<https://smashingmagazine.com/2026/05/mathematical-layouts-sibling-index-sibling-count/>)

Author: hello@smashingmagazine.com (Durgesh Pawar)

Published: 2026-05-21T08:00:00Z

Content type: article

Language: en

Sources: [Articles on Smashing Magazine -- For Web Designers And Developers](<https://devfeed.tech/sources/articles-on-smashing-magazine-for-web-designers-and-developers.md>)

Topics: [Web platform](<https://devfeed.tech/topics/web-platform.md>), [Web Development](<https://devfeed.tech/topics/web-development.md>)

Tags: [animation](<https://devfeed.tech/tags/animation.md>), [browser](<https://devfeed.tech/tags/browser.md>), [coding](<https://devfeed.tech/tags/coding.md>), [css](<https://devfeed.tech/tags/css.md>), [javascript](<https://devfeed.tech/tags/javascript.md>), [selectors](<https://devfeed.tech/tags/selectors.md>), [techniques](<https://devfeed.tech/tags/techniques.md>)

## AI overview

The article explains how CSS sibling-index() and sibling-count() provide numeric sibling positions and totals for calculations such as staggered animation delays, replacing many :nth-child() rules or JavaScript-injected styles.

## Source excerpt

Meet `sibling-index()` and `sibling-count()`. Staggered cascade effect in one line of CSS without `:nth-child()` rules or JS workarounds. Works for 5 items or 5,000.