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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang=en>
<head>
<title>CSS Backgrounds and Borders Module Level 3</title>
<link href=default.css rel=stylesheet type="text/css">
<style type="text/css">
.rhs { white-space: pre-wrap; }
code { font-size: inherit; }
#box-shadow-samples td { background: white; color: black; }
</style>
<link href="http://www.w3.org/StyleSheets/TR/W3C-WD.css" rel=stylesheet
type="text/css">
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1 id=css-backgrounds>CSS Backgrounds and Borders Module Level 3</h1>
<h2 class="no-num no-toc" id=longstatus>W3C Working Draft 9 September 2008</h2>
<dl>
<dt>This version:
<dd><a
href="http://www.w3.org/TR/2008/WD-css3-background-20080909">http://www.w3.org/TR/2008/WD-css3-background-20080909</a></dd>
<!-- <a href="http://dev.w3.org/csswg/css3-background">http://dev.w3.org/csswg/css3-background</a> -->
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-background">http://www.w3.org/TR/css3-background</a>
<dt>Previous versions:
<dd><a
href="http://www.w3.org/TR/2005/WD-css3-background-20050216">http://www.w3.org/TR/2005/WD-css3-background-20050216</a>
<dd><a
href="http://www.w3.org/TR/2002/WD-css3-border-20021107">http://www.w3.org/TR/2002/WD-css3-border-20021107</a>
<dt id=editors-list>Editors:
<dd><a href="mailto:bert@w3.org">Bert Bos</a> (<a
href="http://www.w3.org/">W3C</a>)
<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a>
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2008 <a
href="http://www.w3.org/"><acronym title="World Wide Web
Consortium">W3C</acronym></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute
of Technology">MIT</acronym></a>, <a
href="http://www.ercim.org/"><acronym title="European Research Consortium
for Informatics and Mathematics">ERCIM</acronym></a>, <a
href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p>CSS is a language for describing the rendering of structured documents
(such as HTML and XML) on screen, on paper, in speech, etc. This draft
contains the features of CSS level 3 relating to borders and
backgrounds. It includes and extends the functionality of CSS level 2
<a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>, which
builds on CSS level 1 <a href="#CSS1"
rel=biblioentry>[CSS1]<!--{{CSS1}}--></a>. The main extensions compared to
level 2 are borders consisting of images, boxes with multiple
backgrounds, boxes with rounded corners and boxes with shadows.
<p>This module replaces two earlier drafts: CSS3 Backgrounds and CSS3
Border.
<h2 class="no-num no-toc" id=status>Status of this document</h2>
<!--begin-status-->
<p><em>This section describes the status of this document at the time of
its publication. Other documents may supersede this document. A list of
current W3C publications and the latest revision of this technical report
can be found in the <a href="http://www.w3.org/TR/">W3C technical reports
index at http://www.w3.org/TR/.</a></em>
<p>Publication as a Working Draft does not imply endorsement by the W3C
Membership. This is a draft document and may be updated, replaced or
obsoleted by other documents at any time. It is inappropriate to cite this
document as other than work in progress.
<p>The (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a href="mailto:www-style@w3.org">www-style@w3.org</a> (see
<a href="http://www.w3.org/Mail/Request">instructions</a>) is preferred
for discussion of this specification. When sending e-mail, please put the
text “css3-background” in the subject, preferably like this:
“[<!---->css3-background<!---->] <em>…summary of
comment…</em>”
<p>This document was produced by the <a
href="http://www.w3.org/Style/CSS/members">CSS Working Group</a> (part of
the <a href="http://www.w3.org/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February
2004 W3C Patent Policy</a>. W3C maintains a <a
href="http://www.w3.org/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual
knowledge of a patent which the individual believes contains <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
6 of the W3C Patent Policy</a>.</p>
<!--end-status-->
<p><strong>Not all the corrections and clarifications in the revised
edition of CSS2 <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> have been applied to this
draft yet. In case of conflict (other than on properties and values that
are clearly new to CSS3), CSS 2.1 probably represents the intention
of the CSS WG better than this draft.</strong>
<p class=issue>The CSS WG maintains an <a
href="http://www.w3.org/Style/CSS/Tracker/products/11">issues list</a> for
this module.
<p>The following features are at-risk and may be dropped at the end of the
CR period: inner shadows for ‘<code class=property><a
href="#box-shadow">box-shadow</a></code>’, ‘<code class=css><a
href="#no-clip">no-clip</a></code>’ keyword for ‘<code
class=property><a
href="#background-clip">background-clip</a></code>’.
<h2 class="no-num no-toc" id=contents>Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
<li><a href="#values"><span class=secno>2. </span>Values</a>
<li><a href="#background"><span class=secno>3. </span>Background
properties</a>
<ul class=toc>
<li><a href="#layering"><span class=secno>3.1 </span>Layering multiple
background images</a>
<li><a href="#the-background-color"><span class=secno>3.2 </span>The
‘<code class=property>background-color</code>’ property</a>
<li><a href="#the-background-image"><span class=secno>3.3 </span>The
‘<code class=property>background-image</code>’ property</a>
<li><a href="#the-background-repeat"><span class=secno>3.4 </span>The
‘<code class=property>background-repeat</code>’
property</a>
<li><a href="#the-background-attachment"><span class=secno>3.5
</span>The ‘<code
class=property>background-attachment</code>’ property</a>
<li><a href="#the-background-position"><span class=secno>3.6 </span>The
‘<code class=property>background-position</code>’
property</a>
<li><a href="#the-background-clip"><span class=secno>3.7 </span>The
‘<code class=property>background-clip</code>’ property</a>
<li><a href="#the-background-origin"><span class=secno>3.8 </span>The
‘<code class=property>background-origin</code>’
property</a>
<li><a href="#the-background-size"><span class=secno>3.9 </span>The
‘<code class=property>background-size</code>’ property</a>
<li><a href="#the-background-break"><span class=secno>3.10 </span>The
‘<code class=property>background-break</code>’ property</a>
<li><a href="#the-background"><span class=secno>3.11 </span>The
‘<code class=property>background</code>’ shorthand
property</a>
<li><a href="#the-background0"><span class=secno>3.12 </span>The
background of the canvas</a>
</ul>
<li><a href="#border"><span class=secno>4. </span>Border properties</a>
<ul class=toc>
<li><a href="#the-border-color"><span class=secno>4.1 </span>The
‘<code class=property>border-color</code>’ properties</a>
<li><a href="#the-border-style"><span class=secno>4.2 </span>The
‘<code class=property>border-style</code>’ properties</a>
<li><a href="#the-border-width"><span class=secno>4.3 </span>The
‘<code class=property>border-width</code>’ properties</a>
<li><a href="#the-border-image"><span class=secno>4.4 </span>The
‘<code class=property>border-image</code>’ property</a>
<li><a href="#the-border-radius"><span class=secno>4.5 </span>The
‘<code class=property>border-radius</code>’ properties</a>
<li><a href="#the-border-break"><span class=secno>4.6 </span>The
‘<code class=property>border-break</code>’ property</a>
<li><a href="#the-border-shorthands"><span class=secno>4.7 </span>The
‘<code class=property>border-top</code>’, ‘<code
class=property>border-bottom</code>’, ‘<code
class=property>border-right</code>’, ‘<code
class=property>border-left</code>’, and ‘<code
class=property>border</code>’ properties</a>
<li><a href="#the-box-shadow"><span class=secno>4.8 </span>The
‘<code class=property>box-shadow</code>’ property</a>
</ul>
<li><a href="#definitions"><span class=secno>5. </span>Definitions</a>
<ul class=toc>
<li><a href="#profiles"><span class=secno>5.1 </span>Profiles</a>
<li><a href="#conformance"><span class=secno>5.2 </span>Conformance</a>
<li><a href="#glossary"><span class=secno>5.3 </span>Glossary</a>
<li><a href="#exit"><span class=secno>5.4 </span>CR exit criteria</a>
</ul>
<li><a href="#acknowledgments"><span class=secno>6.
</span>Acknowledgments</a>
<li><a href="#references"><span class=secno>7. </span>References</a>
<ul class=toc>
<li class=no-num><a href="#normative">Normative references</a>
<li class=no-num><a href="#other">Other references</a>
</ul>
<li class=no-num><a href="#property">Property index</a>
<li class=no-num><a href="#index">Index</a>
</ul>
<!--end-toc-->
<h2 id=introduction><span class=secno>1. </span>Introduction</h2>
<p><em>This section is not normative.</em>
<p>When elements are rendered according to the <a
href="http://www.w3.org/TR/CSS21/box.html">CSS box model</a> <a
href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>, each element
is either not displayed at all, or formatted as one or more rectangular
boxes. Each box has a rectangular content area, a band of padding around
the content, a border around the padding, and a margin outside the border.
(The margin may actually be negative, but margins have no influence on the
background and border.)
<div class=figure>
<p><img alt="Diagram of a typical box, showing the content, padding,
border and margin areas" src=box>
<p class=caption>The various areas and edges of a typical box. (This
diagram is explained in the CSS2.1 Box Model chapter <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.)
</div>
<p>The child elements of an element usually create boxes of their own, that
are placed inside the content area of their parent, although they may also
be placed outside it.
<p>The reason an element may result in more than one box, is that elements
may be broken at the end of a line (for inline elements), at the end of a
column or at the end of a page and create further boxes in the next line,
column or page.
<p>The properties of this module deal with the contents of the border area
and with the background of the content, padding and border areas.
<p>That background may be fully transparent (the default), or it may be
filled with a color, one or more images, or both images and color. The
background properties specify what color ( ‘<code class=property><a
href="#background-color">background-color</a></code>’) and images (
‘<code class=property><a
href="#background-image">background-image</a></code>’) to use, where
they are placed ( ‘<code class=property><a
href="#background-position">background-position</a></code>’),
whether they are repeated or scaled ( ‘<code class=property><a
href="#background-repeat">background-repeat</a></code>’,
‘<code class=property><a
href="#background-size">background-size</a></code>’), etc.
<p>The ‘<code class=property><a
href="#border-image">border-image</a></code>’ property can also
define a background image, which, if present, is added on top of that of
the background properties.
<p>The border can either be a predefined style (solid line, double line,
dotted line, pseudo-3D border, etc.) or it can be an image. In the former
case, three properties define the style of the four border sides (
‘<code class=property><a
href="#border-style">border-style</a></code>’), color ( ‘<code
class=property><a href="#border-color">border-color</a></code>’) and
thickness ( ‘<code class=property><a
href="#border-width">border-width</a></code>’). In the latter case,
the sides and corners are taken from the sides and corners of an image
specified with ‘<code class=property><a
href="#border-image">border-image</a></code>’. The image can be
sliced, scaled and stretched in various ways to fit the size of the
border.
<p>If an element is broken into multiple boxes, ‘<code
class=property><a href="#border-break">border-break</a></code>’ and
‘<code class=property><a
href="#background-break">background-break</a></code>’ define how the
borders and background are divided over the various boxes.
<p>There is also another kind of decoration that can be added to an
element: a drop shadow, via the ‘<code class=property><a
href="#box-shadow">box-shadow</a></code>’ property.
<h2 id=values><span class=secno>2. </span>Values</h2>
<p>This specification follows the <a
href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property
definition conventions</a> from <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
<p>‘<code class=css><color></code>’ values are defined in
CSS Color Level 3 <a href="#CSS3COLOR"
rel=biblioentry>[CSS3COLOR]<!--{{!CSS3COLOR}}--></a>.
<p>‘<code class=css><image></code>’ values are defined by
this specification as ‘<code class=css><uri></code>’. (A
future specification may expand the definition of ‘<code
class=css><image></code>’ to allow other values, e.g. to
define image slices.)
<p>All other values are defined in CSS Level 2 Revision 1 <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
<h2 id=background><span class=secno>3. </span>Background properties</h2>
<h3 id=layering><span class=secno>3.1 </span>Layering multiple background
images</h3>
<p>The background of a box can have multiple layers in CSS3. The properties
‘<code class=property><a
href="#background-image">background-image</a></code>’, ‘<code
class=property><a
href="#background-origin">background-origin</a></code>’,
‘<code class=property><a
href="#background-clip">background-clip</a></code>’, ‘<code
class=property><a
href="#background-repeat">background-repeat</a></code>’,
‘<code class=property><a
href="#background-size">background-size</a></code>’, and
‘<code class=property><a
href="#background-position">background-position</a></code>’ may have
multiple comma-separated values. If the values are specified as follows:
<blockquote>
<p>background-image: <var>w</var><sub>1</sub>, <var>w</var><sub>2</sub>,
<var>w</var><sub>3</sub>,…,
<var>w</var><sub><var>M</var></sub><br>
background-repeat: <var>x</var><sub>1</sub>, <var>x</var><sub>2</sub>,
<var>x</var><sub>3</sub>,…,
<var>x</var><sub><var>R</var></sub><br>
background-size: <var>y</var><sub>1</sub>, <var>y</var><sub>2</sub>,
<var>y</var><sub>3</sub>,…,
<var>y</var><sub><var>S</var></sub><br>
background-position: <var>s</var><sub>1</sub>, <var>s</var><sub>2</sub>,
<var>s</var><sub>3</sub>,…, <var>s</var><sub><var>P</var></sub>
</blockquote>
<p>then the number of layers is <var>N</var> = max(<var>M</var>,
<var>R</var>, <var>S</var>, <var>P</var>)
<p>Each of the properties is interpreted as if it had <var>N</var> values,
by repeating the specified values like this:
<blockquote>
<p>background-image:
<var>w</var><sub>1</sub>,…<var>w</var><sub><var>M</var></sub>,
<var>w</var><sub>1</sub>,…<var>w</var><sub><var>M</var></sub>,
<var>w</var><sub>1</sub>,… /* <var>N</var> values */<br>
background-repeat:
<var>x</var><sub>1</sub>,…<var>x</var><sub><var>R</var></sub>,
<var>x</var><sub>1</sub>,…<var>x</var><sub><var>R</var></sub>,
<var>x</var><sub>1</sub>,… /* <var>N</var> values */<br>
background-size:
<var>y</var><sub>1</sub>,…<var>y</var><sub><var>S</var></sub>,
<var>y</var><sub>1</sub>,…<var>y</var><sub><var>S</var></sub>,
<var>y</var><sub>1</sub>,… /* <var>N</var> values */<br>
background-position:
<var>s</var><sub>1</sub>,…<var>r</var><sub><var>P</var></sub>,
<var>s</var><sub>1</sub>,…<var>r</var><sub><var>P</var></sub>,
<var>s</var><sub>1</sub>,… /* <var>N</var> values */
</blockquote>
<div class=example>
<p>This set of declarations:
<pre>
background-image: url(flower.png), url(ball.png), url(grass.png);
background-position: center center, 20% 80%, top left;
background-origin: border-box, content-box;
</pre>
<p>has exactly the same effect as this set with the origin values repeated
(displayed in bold for clarity):
<pre>
background-image: url(flower.png), url(ball.png), url(grass1.png);
background-position: center center, 20% 80%, top left;
background-origin: border-box, content-box<b>, border-box</b>;
</pre>
<p>Likewise, this set of declarations:
<pre>
background-image: url(red.png), url(blue.png);
background-repeat: repeat-x, repeat-y, repeat-y;
background-position: 20% 25%, 40% 10%, 50% 15%, 70% 40%, 90% 35%;
</pre>
<p>has the same effect as:
<pre>
background-image: url(red.png), url(blue.png)<b>, url(red.png),</b>
<b>url(blue.png), url(red.png)</b>;
background-repeat: repeat-x, repeat-y, repeat-y<b>, repeat-x, repeat-y</b>;
background-position: 20% 25%, 40% 10%, 50% 15%, 70% 40%, 90% 35%;
</pre>
</div>
<p>Each of the images is repeated, sized, and positioned according to the
corresponding value in the other properties. The first image in the list
is the layer closest to the user, the next one is painted behind the
first, and so on. The background color, if present, is painted below all
of the other layers.
<h3 id=the-background-color><span class=secno>3.2 </span>The ‘<code
class=property><a
href="#background-color">background-color</a></code>’ property</h3>
<table class=propdef id=name->
<tbody>
<tr>
<th>Name:
<td><dfn id=background-color>background-color</dfn>
<tr>
<th>Value:
<td><color> [ / <color> ]? | / <color>
<tr>
<th>Initial:
<td>transparent
<tr>
<th>Applies to:
<td>all elements
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>the computed color(s)
</table>
<p>This property sets the background color of an element. The color is
drawn behind any background images. The color after the slash, if present,
is used instead of the first color in the case the element's specified
bottom-most background image, if any, cannot be drawn. This color is
called the <dfn id=fallback>fallback color.</dfn> If the color before the
slash is missing, it is assumed to be ‘<code
class=css>transparent</code>’.
<div class=example>
<p>Example:
<pre>h1 { background-color: #F00 }
div { background-color: / white; } /* Equivalent to background-color: transparent / white; */</pre>
</div>
<p>Both the normal color and the fallback color are clipped according to
the ‘<code class=property><a
href="#background-clip">background-clip</a></code>’ value associated
with the bottom-most background image.
<h3 id=the-background-image><span class=secno>3.3 </span>The ‘<code
class=property><a
href="#background-image">background-image</a></code>’ property</h3>
<table class=propdef id=name-0>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-image>background-image</dfn>
<tr>
<th>Value:
<td>[ <var><image></var> | none ] [ , [ <var><image></var> |
none ] ]*
<tr>
<th>Initial:
<td>none
<tr>
<th>Applies to:
<td>all elements
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>as specified, but with URIs made absolute
</table>
<p>This property sets the background image(s) of an element. Images are
drawn with the first specified one on top (closest to the user) and each
subsequent image behind the previous one.
<p>A value of ‘<code class=css>none</code>’ counts as an image
layer but draws nothing. An image that is empty (zero width or zero
height), that fails to download, or that cannot be displayed (e.g.,
because it is not in a supported image format) has the same effect as
‘<code class=css>none</code>’.
<p>See the section <a href="#layering">“Layering multiple background
images”</a> for how ‘<code class=property><a
href="#background-image">background-image</a></code>’ interacts with
other comma-separated background properties to form each background image
layer.
<div class=example>
<p>Some examples specifying background images:</p>
<pre>
body { background-image: url("marble.svg") }
p { background-image: none }
div { background-image: url(tl.png), url(tr.png) }
</pre>
</div>
<p class=note>Implementations may optimize by not downloading and drawing
images that are not visible (e.g., because they are behind other, fully
opaque images).
<h3 id=the-background-repeat><span class=secno>3.4 </span>The ‘<code
class=property><a
href="#background-repeat">background-repeat</a></code>’ property</h3>
<table class=propdef id=name-1>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-repeat>background-repeat</dfn>
<tr>
<th>Value:
<td><var><a href="#ltrepeatgt"><repeat></a></var> [ , <var><a
href="#ltrepeatgt"><repeat></a></var> ]*
<tr>
<th>Initial:
<td>repeat
<tr>
<th>Applies to:
<td>all elements
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>as specified
</table>
<p>Specifies how background images are tiled after they have been sized and
positioned. The type <dfn id=ltrepeatgt><var><repeat></var></dfn>
stands for:
<pre
class=rhs>repeat-x | repeat-y | [repeat | space | round | no-repeat]{1,2}</pre>
<p>Single values for <var><a href="#ltrepeatgt"><repeat></a></var>
have the following meanings:
<dl>
<dt><dfn id=repeat-x>repeat-x</dfn>
<dd> Equivalent to ‘<code class=css>repeat no-repeat</code>’.
<dt><dfn id=repeat-y>repeat-y</dfn>
<dd> Equivalent to ‘<code class=css>no-repeat repeat</code>’.
<dt><dfn id=repeat-repeat>repeat</dfn>
<dd> Equivalent to ‘<code class=css>repeat repeat</code>’.
<dt><dfn id=no-repeat-no-repeat>no-repeat</dfn>
<dd> Equivalent to ‘<code class=css>no-repeat
no-repeat</code>’
<dt><dfn id=space-space>space</dfn>
<dd> Equivalent to ‘<code class=css>space space</code>’
<dt><dfn id=round-round>round</dfn>
<dd> Equivalent to ‘<code class=css>round round</code>’
</dl>
<p>If a <var><a href="#ltrepeatgt"><repeat></a></var> value has two
keywords, the first one is for the horizontal direction, the second for
the vertical one, as follows:
<p class=issue>Should "positioning area" be "painting area" here or vice
versa?
<dl>
<dt><dfn id=repeat>repeat</dfn>
<dd> The image is repeated in this direction as often as needed to cover
the <a href="#bg-paint-area">background painting area</a>.
<dt><dfn id=no-repeat>no-repeat</dfn>
<dd> The image is placed once and not repeated in this direction.
<dt><dfn id=space>space</dfn>
<dd> The image is repeated as often as will fit within the <a
href="#bg-pos-area">background positioning area</a> without being clipped
and then the images are spaced out to fill the area. The first and last
images touch the edges of the area. If the background painting area is
larger than the background positioning area, then the pattern repeats to
fill the background painting area. The value of ‘<code
class=property><a
href="#background-position">background-position</a></code>’ for
this direction is ignored, unless there is not enough space for two
copies of the image in this direction, in which case only one image is
placed and ‘<code class=property><a
href="#background-position">background-position</a><
16E8
;/code>’
determines its position in this direction.
<dt><dfn id=round>round</dfn>
<dd> The image is repeated as often as will fit within the <a
href="#bg-pos-area">background positioning area</a>. If it doesn't fit a
whole number of times, it is reduced in size until it does. See
explanation under ‘<code class=property><a
href="#background-size">background-size</a></code>’. If the
background painting area is larger than the background positioning area,
then the pattern repeats to fill the background painting area.
</dl>
<p>Unless one of the two keywords is ‘<code class=css><a
href="#no-repeat">no-repeat</a></code>’, the whole background
painting area will be tiled, i.e., not just one vertical strip and one
horizontal strip.
<div class=example>
<p style=display:none>Example(s):
<pre>
body {
background: white url("pendant.png");
background-repeat: repeat-y;
background-position: center;
}
</pre>
<div class=figure>
<p><img alt="A centered background image, with copies repeated up and
down the border, padding and content areas."
src=bg-repeat><!--<SPAN class="dlink"> <A
name="img-bg-repeat" href="images/longdesc/bg-repeat-desc.html"
title="Long description for background pattern">[D]</A></SPAN>-->
<p class=caption>The effect of ‘<code class=css><a
href="#repeat-y">repeat-y</a></code>’: One copy of the background
image is centered, and other copies are put above and below it to make a
vertical band behind the element.
</div>
</div>
<div class=example>
<p style=display:none>Example(s):
<pre>
body {
background-image: url(dot.png) white;
background-repeat: space
}
</pre>
<div class=figure>
<p><img alt="Image of an element with a dotted background" src=bg-space>
<p class=caption>The effect of ‘<code class=property><a
href="#space">space</a></code>’: the image of a dot is tiled to
cover the whole background and the images are equally spaced.
</div>
</div>
<p>See the section <a href="#layering">“Layering multiple background
images”</a> for how ‘<code class=property><a
href="#background-repeat">background-repeat</a></code>’ interacts
with other comma-separated background properties to form each background
image layer.
<h3 id=the-background-attachment><span class=secno>3.5 </span>The
‘<code class=property><a
href="#background-attachment">background-attachment</a></code>’
property</h3>
<table class=propdef id=name-2>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-attachment>background-attachment</dfn>
<tr>
<th>Value:
<td>scroll | fixed | local [, scroll | fixed | local]*
<tr>
<th>Initial:
<td>scroll
<tr>
<th>Applies to:
<td>all elements
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>as specified
</table>
<p>If background images are specified, this property specifies whether they
are fixed with regard to the <em class=index id=viewport>viewport</em>
(‘<code class=css>fixed</code>’) scroll along with the element
(‘<code class=css>scroll</code>’ and ‘<code
class=css>local</code>’).
<p>The difference between ‘<code class=css>scroll</code>’ and
‘<code class=css>local</code>’ is only visible when the
element has a scrolling mechanism (see the ‘<code
class=property>overflow</code>’ property <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>): in the case of ‘<code
class=css>scroll</code>’, the background does not scroll with the
element's content. (It is attached to the element's border, as it were.)
In the case of ‘<code class=css>local</code>’, the background
scrolls along with the element's content. In this case, the background
behind the element's border (if any) scrolls as well, even though the
border itself does not scroll with the contents. The UA may, however,
treat the ‘<code class=css><a
href="#no-clip">no-clip</a></code>’ and ‘<code class=css><a
href="#border-box">border-box</a></code>’ values of ‘<code
class=property><a
href="#background-clip">background-clip</a></code>’ as ‘<code
class=css><a href="#padding-box">padding-box</a></code>’ in cases
where ‘<code class=property><a
href="#background-attachment">background-attachment</a></code>’ is
‘<code class=css>local</code>’ and the contents of the element
scroll.
<p>Even if the image is fixed, it is still only visible when it is in the
<a href="#bg-paint-area">background painting area</a> of the element or
otherwise unclipped. Thus, unless the image is tiled, it may be invisible.
<div class=example>
<p>This example creates an infinite vertical band that remains “glued”
to the viewport when the element is scrolled.
<pre>
body {
background: red url("pendant.gif");
background-repeat: repeat-y;
background-attachment: fixed;
}
</pre>
</div>
<p>User agents that do not support ‘<code
class=css>fixed</code>’ backgrounds (for example due to limitations
of the hardware platform) should ignore declarations with the keyword
‘<code class=css>fixed</code>’. For example:
<pre class=example>
body {
/* For all UAs: */
background: white url(paper.png) scroll;
/* For UAs that do fixed backgrounds: */
background: white url(ledger.png) fixed;
}
h1 {
/* For all UAs: */
background: silver;
/* For UAs that do fixed backgrounds: */
background: url(stripe.png) fixed, white url(ledger.png) fixed;
}
</pre>
<p>See the section <a href="#layering">“Layering multiple background
images”</a> for how ‘<code class=property><a
href="#background-attachment">background-attachment</a></code>’
interacts with other comma-separated background properties to form each
background image layer.
<h3 id=the-background-position><span class=secno>3.6 </span>The
‘<code class=property><a
href="#background-position">background-position</a></code>’ property</h3>
<table class=propdef id=name-3>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-position>background-position</dfn>
<tr>
<th>Value:
<td><var><a href="#ltbg-positiongt"><bg-position></a></var> [ ,
<var><a href="#ltbg-positiongt"><bg-position></a></var> ]*
<tr>
<th>Initial:
<td>0% 0%
<tr>
<th>Applies to:
<td>all elements
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>refer to size of background positioning area <em>minus</em> size of
background image; see text
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>If one or two values are specified, for a <length> the
absolute value, otherwise a percentage. If three or four values are
specified, two pairs of a keyword plus a length or percentage.
</table>
<p>If background images have been specified, this property specifies their
initial position within their corresponding <a
href="#bg-pos-area">background positioning area</a>.
<p class=syntax>The <dfn
id=ltbg-positiongt><var><bg-position></var></dfn> stands for:
<pre class=rhs>[
[ [ <var><a href="#position-percentage"><percentage></a></var> | <var><a href="#position-length"><length></a></var> | left | center | right ] ]
[ [ <var><a href="#position-percentage"><percentage></a></var> | <var><a href="#position-length"><length></a></var> | top | center | bottom ] ]?
|
[ center | [ left | right ] [ <var><a href="#position-percentage"><percentage></a></var> | <var><a href="#position-length"><length></a></var> ]? ] ||
[ center | [ top | bottom ] [ <var><a href="#position-percentage"><percentage></a></var> | <var><a href="#position-length"><length></a></var> ]? ]
]</pre>
<p>If only one value is specified, the second value is assumed to be
‘<code class=property><a
href="#position-center">center</a></code>’. If two values are given
and at least one value is not a keyword, then the first value represents
the horizontal position (or offset) and the second represents the vertical
position (or offset). <percentage> and <length> values here
represent an offset of the top left corner of the background image from
the top left corner of the background positioning area.
<p>If three or four values are given, then each <percentage> or
<length> represents an offset and must be preceded by a keyword,
which specifies from which edge the offset is given. For example,
‘<code class=css>background-position: bottom 10px right
20px</code>’ represents a ‘<code class=css>10px</code>’
vertical offset up from the bottom edge and a ‘<code
class=css>20px</code>’ horizontal offset leftward from the right
edge. If three values are given, the missing offset is assumed to be zero.
<p>Positive values represent an offset <em>inward</em> from the edge of the
background positioning area. Negative values represent an offset
<em>outward</em> from the edge of the background positioning area.