:nth-child()The :nth-child() and :nth-last-child() CSS functional pseudo-classes match elements based on their index within a list of elements. The :first-child and :last-child pseudo-classes match the first and last element in a list, and the :only-child pseudo-class matches an element with no siblings.selectorsSelectorswidely2015-07-292018-01-29https://drafts.csswg.org/selectors-3/#nth-child-pseudohttps://drafts.csswg.org/selectors-3/#nth-last-child-pseudohttps://developer.mozilla.org/docs/Web/CSS/Reference/Selectors/:nth-childcss.selectors.first-childcss.selectors.first-child.no_parent_requiredcss.selectors.last-childcss.selectors.last-child.no_parent_requiredcss.selectors.nth-childcss.selectors.nth-child.no_parent_requiredcss.selectors.nth-last-childcss.selectors.nth-last-child.no_parent_requiredcss.selectors.only-childcss.selectors.only-child.no_parent_requiredhttps://nowyoucanuse.com/features--nth-child.html