This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

This is a property of the original CSS Flexible Box Layout Module draft, and has been replaced by a newer standard. See flexbox for information about the current standard.

The -moz-box-pack and -webkit-box-pack CSS properties specify how a -moz-box or -webkit-box packs its contents in the direction of its layout. The effect of this is only visible if there is extra space in the box.

/* Keyword values */
box-pack: start;
box-pack: center;
box-pack: end;
box-pack: justify;

/* Global values */
box-pack: inherit;
box-pack: initial;
box-pack: unset;

The direction of layout depends on the element's orientation: horizontal or vertical.

Initial valuestart
Applies toelements with a CSS display value of -moz-box, -moz-inline-box, -webkit-box or -webkit-inline-box
Computed valueas specified
Animation typediscrete
Canonical orderthe unique non-ambiguous order defined by the formal grammar


The box-pack property is specified as one of the keyword values listed below.


The box packs contents at the start, leaving any extra space at the end.
The box packs contents in the center, dividing any extra space equally between the start and the end.
The box packs contents at the end, leaving any extra space at the start.
The space is divided evenly in-between each child, with none of the extra space placed before the first child or after the last child. If there is only one child, treat the value as if it were start.

Formal syntax

start | center | end | justify


div.example {
  border-style: solid;

  display: -moz-box; /* Mozilla */
  display: -webkit-box; /* WebKit */

  /* Make this box taller than the children, 
     so there is room for the box-pack */
  height: 300px;
  /* Make this box wide enough to show the contents 
     are centered horizontally */
  width: 300px;
  /* Children should be oriented vertically */
  -moz-box-orient: vertical; /* Mozilla */
  -webkit-box-orient: vertical; /* WebKit */

  /* Align children to the horizontal center of this box */
  -moz-box-align: center; /* Mozilla */
  -webkit-box-align: center; /* WebKit */

  /* Pack children to the bottom of this box */
  -moz-box-pack: end;             /* Mozilla */
  -webkit-box-pack: end;          /* WebKit */

div.example p {
  /* Make children narrower than their parent,
     so there is room for the box-align */
  width: 200px;
<div class="example">
  <p>I will be second from the bottom of div.example, centered horizontally.</p>
  <p>I will be on the bottom of div.example, centered horizontally.</p>


The edge of the box designated the start for packing purposes depends on the box's orientation and direction:

  Normal Reverse
Horizontal left right
Vertical top bottom

The edge opposite to the start is designated the end.

If the packing is set using the element's pack attribute, then the style is ignored.


This property is non-standard, though a similar property appeared in an early draft of CSS3 Flexbox, which has been superseded in newer versions of the specification.

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support Yes -webkit- 12 -webkit-

Yes -moz-

49 -webkit-

48 -webkit- 1

No Yes -webkit-

3 -webkit-

1.1 -khtml-

FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support ? ? Yes -webkit-

Yes -moz-

49 -webkit-

48 -webkit- 1

?1 -webkit- ?

1. From version 48: this feature is behind the layout.css.prefixes.webkit preference (needs to be set to true). To change preferences in Firefox, visit about:config.

See also

box-orient, box-direction, box-align

Document Tags and Contributors

Last updated by: fscholz,