:nth-child() - CSS: Cascading Style Sheets 编辑

The :nth-child() CSS pseudo-class matches elements based on their position in a group of siblings.

/* Selects the second <li> element in a list */
li:nth-child(2) {
  color: lime;
}

/* Selects every fourth element
   among any group of siblings */
:nth-child(4n) {
  color: lime;
}

Syntax

:nth-child() takes a single argument that describes a pattern for matching element indices in a list of siblings. Element indices are 1-based.

Keyword values

odd

Represents elements whose numeric position in a series of siblings is odd: 1, 3, 5, etc.

even

Represents elements whose numeric position in a series of siblings is even: 2, 4, 6, etc.

Functional notation

<An+B>

Represents elements in a list whose indices match those found in a custom pattern of numbers, defined by An+B, where:
A is an integer step size,
B is an integer offset,
n is all positive integers, starting from 0.

It can be read as the An+Bth element of a list.

Formal syntax

:nth-child( <nth> [ of <complex-selector-list> ]? )
where 
<nth> = <an-plus-b> | even | odd
<complex-selector-list> = <complex-selector>#
where 
<complex-selector> = <compound-selector> [ <combinator>? <compound-selector> ]*
where 
<compound-selector> = [ <type-selector>? <subclass-selector>* [ <pseudo-element-selector> <pseudo-class-selector>* ]* ]!
<combinator> = '>' | '+' | '~' | [ '||' ]
where 
<type-selector> = <wq-name> | <ns-prefix>? '*'
<subclass-selector> = <id-selector> | <class-selector> | <attribute-selector> | <pseudo-class-selector>
<pseudo-element-selector> = ':' <pseudo-class-selector>
<pseudo-class-selector> = ':' <ident-token> | ':' <function-token> <any-value> ')'
where 
<wq-name> = <ns-prefix>? <ident-token>
<ns-prefix> = [ <ident-token> | '*' ]?  | 
<id-selector> = <hash-token>
<class-selector> = '.' <ident-token>
<attribute-selector> = '[' <wq-name> ']' | '[' <wq-name> <attr-matcher> [ <string-token> | <ident-token> ] <attr-modifier>? ']'
where 
<attr-matcher> = [ '~' |  |  | '^' | '$' | '*' ]? '='
<attr-modifier> = i | s

Examples

Example selectors

tr:nth-child(odd) or tr:nth-child(2n+1)

Represents the odd rows of an HTML table: 1, 3, 5, etc.

tr:nth-child(even) or tr:nth-child(2n)

Represents the even rows of an HTML table: 2, 4, 6, etc.

:nth-child(7)

Represents the seventh element.

:nth-child(5n)

Represents elements 5 [=5×1], 10 [=5×2], 15 [=5×3], etc. The first one to be returned as a result of the formula is 0 [=5x0], resulting in a no-match, since the elements are indexed from 1, whereas n starts from 0. This may seem weird at first, but it makes more sense when the B part of the formula is >0, like in the next example.

:nth-child(n+7)

Represents the seventh and all following elements: 7 [=0+7], 8 [=1+7], 9 [=2+7], etc.

:nth-child(3n+4)

Represents elements 4 [=(3×0)+4], 7 [=(3×1)+4], 10 [=(3×2)+4], 13 [=(3×3)+4], etc.

:nth-child(-n+3)

Represents the first three elements. [=-0+3, -1+3, -2+3]

p:nth-child(n)

Represents every <p> element in a group of siblings. This selects the same elements as a simple p selector (although with a higher specificity).

p:nth-child(1) or p:nth-child(0n+1)

Represents every <p> that is the first element in a group of siblings. This is the same as the :first-child selector (and has the same specificity).

p:nth-child(n+8):nth-child(-n+15)

Represents the eighth through the fifteenth <p> elements of a group of siblings.

Detailed example

HTML

<h3><code>span:nth-child(2n+1)</code>, WITHOUT an
   <code>&lt;em&gt;</code> among the child elements.</h3>
<p>Children 1, 3, 5, and 7 are selected.</p>
<div class="first">
  <span>Span 1!</span>
  <span>Span 2</span>
  <span>Span 3!</span>
  <span>Span 4</span>
  <span>Span 5!</span>
  <span>Span 6</span>
  <span>Span 7!</span>
</div>

<br>

<h3><code>span:nth-child(2n+1)</code>, WITH an
   <code>&lt;em&gt;</code> among the child elements.</h3>
<p>Children 1, 5, and 7 are selected.<br>
   3 is used in the counting because it is a child, but it isn't
   selected because it isn't a <code>&lt;span&gt;</code>.</p>
<div class="second">
  <span>Span!</span>
  <span>Span</span>
  <em>This is an `em`.</em>
  <span>Span</span>
  <span>Span!</span>
  <span>Span</span>
  <span>Span!</span>
  <span>Span</span>
</div>

<br>

<h3><code>span:nth-of-type(2n+1)</code>, WITH an
   <code>&lt;em&gt;</code> among the child elements.</h3>
<p>Children 1, 4, 6, and 8 are selected.<br>
   3 isn't used in the counting or selected because it is an <code>&lt;em&gt;</code>,
   not a <code>&lt;span&gt;</code>, and <code>nth-of-type</code> only selects
   children of that type. The <code>&lt;em&gt;</code> is completely skipped
   over and ignored.</p>
<div class="third">
  <span>Span!</span>
  <span>Span</span>
  <em>This is an `em`.</em>
  <span>Span!</span>
  <span>Span</span>
  <span>Span!</span>
  <span>Span</span>
  <span>Span!</span>
</div>

CSS

html {
  font-family: sans-serif;
}

span,
div em {
  padding: 5px;
  border: 1px solid green;
  display: inline-block;
  margin-bottom: 3px;
}

.first span:nth-child(2n+1),
.second span:nth-child(2n+1),
.third span:nth-of-type(2n+1) {
  background-color: lime;
}

Result

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• :nth-of-type, :nth-last-child