ElementnthchildAnB
ElementnthchildAnB refers to the CSS structural pseudo-class :nth-child(an+b), a formula used to select elements based on their position among siblings. The selector matches elements whose index i (starting at 1) can be expressed as i = an + b for some integer n ≥ 0. Here a and b are integers; a may be zero or negative. When a is zero, the selector targets only the element at position b (if that position exists).
- :nth-child(2n) selects every second element: positions 2, 4, 6, …
- :nth-child(2n+1) selects odd positions: 1, 3, 5, …
- :nth-child(-n+3) selects the first three elements: 1, 2, 3
- :nth-child(3) selects only the third element
- The index is counted among all siblings, regardless of element type. To target specific element types,
- The formula supports negative and positive values; for many practical patterns, users commonly see positive a
- Examples are widely used for styling lists, tables, and layout patterns where consistent alternating or grouped
- Broader browser support is standard across modern browsers; performance is generally adequate for typical document structures.
- :nth-of-type, which uses a similar formula but counts only elements of the same type
- Other functional pseudo-classes for structural styling and pattern-based selection
- CSS selectors level 3 and 4 specifications provide the formal definitions and expanded syntax for these