:nth-child(N) (CSS selector)

This pseudo-class matches elements on the basis of their positions within a parent element’s list of child elements.

The pseudo-class accepts an argument, N, which can be a keyword, a number, or a number expression of the form an+b. For more information, see Understanding :nth-child Pseudo-class Expressions.

If N is a number or a number expression, :nth-child(N) matches elements that are preceded by N-1 siblings in the document tree.

The following example selectors are equivalent, and will match odd-numbered table rows:

tr:nth-child(2n+1) {
⋮ declarations
}
tr:nth-child(odd) {
⋮ declarations
}


This example selector will match the first three rows of any table:

tr:nth-child(-n+3) {
⋮ declarations
}


This example selector will match any paragraph that’s the first child element of its parent element:

p:nth-child(1) {
⋮ declarations
}


This is, of course, equivalent to the selector p:first-child:

tr:nth-child(odd) {
⋮ declarations
}