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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>CSS3 Backgrounds and Borders Module</title>
<link href="../default.css" rel=stylesheet type="text/css">
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<body>
<div class=head>
<p><a href="http://www.w3.org/"><img alt=W3C height=48 name=w3cLogo
src="http://www.w3.org/Icons/w3c_home" width=72></a>
<h1 id=css-backgrounds>CSS Backgrounds and Borders Module Level 3</h1>
<h2 class="no-num no-toc" id=w3c-working>W3C Working Draft 18 January 2008</h2>
<dl>
<dt>This version:
<dd><a
href="http://www.w3.org/TR/2008/ED-css3-background-20080118">http://www.w3.org/TR/2008/ED-css3-background-20080118</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:frederick.boland@nist.gov">Tim Boland</a> (<a
href="http://www.nist.gov/">NIST</a>)
<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>This is a public copy of the editors' draft. It is provided for
discussion only and may change at any moment. It probably contains errors.
Its publication here does not imply endorsement of its contents by W3C.
<!--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>
<h2 class="no-num no-toc" id=contents>Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#dependencies"><span class=secno>1. </span>Dependencies with
other CSS 3 Modules</a>
<li><a href="#context"><span class=secno>2. </span>Context</a>
<ul class=toc>
<li><a href="#modularization"><span class=secno>2.1.
</span>Modularization of CSS</a>
<li><a href="#changesFromCSS2"><span class=secno>2.2. </span>Changes
from CSS 2.1</a>
</ul>
<li><a href="#the-layout"><span class=secno>3. </span>The layout model of
backgrounds and borders</a>
<li><a href="#background"><span class=secno>4. </span>Background
properties</a>
<ul class=toc>
<li><a href="#the-background-color"><span class=secno>4.1. </span>The
'background-color' property</a>
<li><a href="#the-background-image"><span class=secno>4.2. </span>The
'background-image' property</a>
<li><a href="#the-background-repeat"><span class=secno>4.3. </span>The
'background-repeat' property</a>
<li><a href="#the-background-attachment"><span class=secno>4.4.
</span>The 'background-attachment' property</a>
<li><a href="#the-background-position"><span class=secno>4.5. </span>The
'background-position' property</a>
<li><a href="#the-background-clip"><span class=secno>4.6.
5DB9
</span>The
'background-clip' property</a>
<li><a href="#the-background-origin"><span class=secno>4.7. </span>The
'background-origin' property</a>
<li><a href="#the-background-size"><span class=secno>4.8. </span>The
'background-size' property</a>
<li><a href="#the-background-break"><span class=secno>4.9. </span>The
'background-break' property</a>
<li><a href="#layering"><span class=secno>4.10. </span>Layering multiple
background images</a>
<li><a href="#the-background-shadow"><span class=secno>4.11. </span>The
'background-shadow' property</a>
<li><a href="#the-background"><span class=secno>4.12. </span>The
'background' property</a>
<li><a href="#the-background0"><span class=secno>4.13. </span>The
background of the canvas</a>
</ul>
<li><a href="#border"><span class=secno>5. </span>Border properties</a>
<ul class=toc>
<li><a href="#the-border-color"><span class=secno>5.1. </span>The
'border-color' properties</a>
<li><a href="#the-border-style"><span class=secno>5.2. </span>The
'border-style' properties</a>
<li><a href="#the-border-width"><span class=secno>5.3. </span>The
'border-width' properties</a>
<li><a href="#the-border-image"><span class=secno>5.4. </span>The
'border-image' property</a>
<li><a href="#the-border-radius"><span class=secno>5.5. </span>The
'border-radius' properties</a>
<li><a href="#the-border-break"><span class=secno>5.6. </span>The
'border-break' property</a>
<li><a href="#the-border-shorthands"><span class=secno>5.7. </span>The
'border-top', 'border-bottom', 'border-right', 'border-left', and
'border' properties</a>
<li><a href="#the-border-shadow"><span class=secno>5.8. </span>The
'border-shadow' property</a>
</ul>
<li><a href="#definitions"><span class=secno>6. </span>Definitions</a>
<ul class=toc>
<li><a href="#profiles"><span class=secno>6.1. </span>Profiles</a>
<li><a href="#conformance"><span class=secno>6.2. </span>Conformance</a>
<li><a href="#glossary"><span class=secno>6.3. </span>Glossary</a>
<li><a href="#exit"><span class=secno>6.4. </span>CR exit criteria</a>
</ul>
<li><a href="#acknowledgments"><span class=secno>7.
</span>Acknowledgments</a>
<li><a href="#references"><span class=secno>8. </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=dependencies><span class=secno>1. </span>Dependencies with other CSS
3 Modules</h2>
<ul><!--<li>General Syntax [!CSS3SYN]-->
<li>Values and Units <a href="#CSS3VAL"
rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a> (in particular the types
<dfn id=ltlengthgt><var><length></var><
AE07
/dfn>, <dfn
id=lturigt><var><uri></var></dfn> and <dfn
id=ltpercentagegt><var><percentage></var></dfn>)
<!--<li>Cascading and Inheritance [!CSS3CASCADE]-->
<!--<li>Box Model [!CSS3BOX]-->
<li>CSS 2.1 <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> (in particular the box model
of section 8.1)
<li>Color module <a href="#CSS3COLOR"
rel=biblioentry>[CSS3COLOR]<!--{{!CSS3COLOR}}--></a> (in particular the
<dfn id=ltcolorgt><var><color></var></dfn> type)
<!--<li>User Interface [? check]-->
<!--<li>Absolute Positioning Module [!CSS3POS]] (in particular the
section “Elaborate
description of Stacking Contexts”)-->
<!--<li>Paged Media [!CSS3PAGE] (breaking elements across
pages)-->
</ul>
<h2 id=context><span class=secno>2. </span>Context</h2>
<h3 id=modularization><span class=secno>2.1. </span>Modularization of CSS</h3>
<p>The members of the Cascading Style Sheets (CSS) Working Group proposed
during the Clamart meeting to modularize the CSS specification.
<p>This modularization, and the externalization of the general syntax, of
CSS reduces the size of the specification and allows new types of
specifications to use selectors and/or CSS general syntax.
<p>This module will have its own test suite (on the <a
href="/Style/CSS/Test/">CSS test suites page</a>) with several tests per
concept introduced in this document, as well as tests for multiple
concepts used together. This test suite will not consist of full
conformance tests, but is intended to ensure interoperability between
implementations and forms part of the CR exit criteria.
<p>See the section on <a href="#conformance">Conformance</a> for the role
of modules in the implementation requirements for <a href="#ua"
title=UA>UAs</a>.
<h3 id=changesFromCSS2><span class=secno>2.2. </span>Changes from CSS 2.1</h3>
<p class=issue>[This section needs to be revised.]
<p>'Background-clip', 'background-break', and 'background-origin' are new.
Also there are changes to the 'background' shorthand property.
<p>'Background-attachment' has a new value ''local''.
<p>The background can now have multiple images. As a consequence, several
properties now accept a comma-separated list of values.
<p>'Box-shadow', 'border-image', 'border-break' and 'border-radius' are
new.
<h2 id=the-layout><span class=secno>3. </span>The layout model of
backgrounds and borders</h2>
<p>(This section is not normative.)
<p>When elements are rendered according to the CSS box model <a
href="#CSS3BOX" rel=biblioentry>[CSS3BOX]<!--{{CSS3BOX}}--></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 CSS3 Box Module <a href="#CSS3BOX"
rel=biblioentry>[CSS3BOX]<!--{{CSS3BOX}}--></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 ( 'background-color') and images
( 'background-image') to use, where they are placed (
'background-position'), whether they are repeated or scaled (
'background-repeat', 'background-size'), etc.
<p>The 'border-image' 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 (
'border-style'), color ( 'border-color') and thickness ( 'border-width').
In the latter case, the sides and corners are taken from the sides and
corners of an image specified with 'border-image'. 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, 'border-break' and
'background-break' 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 'background-shadow' property.
<h2 id=background><span class=secno>4. </span>Background properties</h2>
<h3 id=the-background-color><span class=secno>4.1. </span>The
'background-color' property</h3>
<table class=propdef id=name->
<tbody>
<tr>
<th>Name:
<td><dfn id=background-color>background-color</dfn>
<tr>
<th>Value:
<th><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>as specified
</table>
<p>This property sets the background color of an element. Valid color
values are defined in the Color Module <a href="#CSS3COLOR"
rel=biblioentry>[CSS3COLOR]<!--{{!CSS3COLOR}}--></a>.
<div class=example>
<p style=display:none>Example(s):
<pre>h1 { background-color: #F00 }</pre>
</div>
<p class=issue>Some people (e.g., Emrah Baskaya and <a
href="http://lists.w3.org/Archives/Public/www-style/2006Aug/0001.html">
Simon Pieters</a>) have argued that there is a need for a fallback color,
which is only shown when any specified image(s) cannot be loaded.
<h3 id=the-background-image><span class=secno>4.2. </span>The
'background-image' 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><a href="#lturigt0"><uri></a></var> | none ] [ , [
<var><a href="#lturigt0"><uri></a></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. The 'background-color' is
painted below all the images.
<p>A value of <span class=css title=bg-none>'none'</span> counts as an
image 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
<span class=css title=bg-image-none>'none'</span>.
<p>See the section <a href="#layering">“Layering multiple background
images”</a> for how each image is tiled or stretched.
<div class=example>
<p style=display:none>Example:
<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).
<p class=issue>Some interoperability in the supported formats would be
nice. Should we say that UAs should support PNG, JPEG and SVG here and
then change the “should” to a “must” in some of
the profiles?
<h3 id=the-background-repeat><span class=secno>4.3. </span>The
'background-repeat' 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 images are tiled. The type <dfn
id=ltrepeatgt><var><repeat></var></dfn> stands for: repeat-x |
repeat-y | [repeat | space | round | no-repeat]{1,2}.
<p>See the section <a href="#layering">“Layering multiple background
images”</a> for how each comma-separated value is applied to each
image of the 'background-image' property.
<p>The tiling and positioning of the background image on inline elements is
described under the 'background-break' property.
<p class=issue>Should there also be values of 'repeat-up', 'repeat-down',
'repeat-right', and 'repeat-left' for this property?
<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 ''repeat no-repeat''.
<dt><dfn id=repeat-y>repeat-y</dfn>
<dd> Equivalent to ''no-repeat repeat''
<dt><a class=css href="#repeat">repeat</a>
<dd> Equivalent to ''repeat repeat''
<dt><a class=css href="#no-repeat">no-repeat</a>
<dd> Equivalent to ''no-repeat no-repeat''
<dt><a class=css href="#space">space</a>
<dd> Equivalent to ''space space''
<dt><a class=css href="#round">round</a>
<dd> Equivalent to ''round round''
</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:
<dl>
<dt><dfn id=repeat>repeat</dfn>
<dd> The image is repeated in this direction as often as needed to cover
the area. The image is clipped at the border or padding edge (depending
on 'background-clip').
<dt><dfn id=no-repeat>no-repeat</dfn>
<dd> The image is not repeated in this direction. If it is too large, the
image is clipped at the border or padding edge (depending on
'background-clip').
<dt><dfn id=space>space</dfn>
<dd> The image is repeated as often as it will fit without being clipped
and then the images are spaced out to fill the area. The space between
the edge and the first image is half the space between each pair of
images. The value of 'background-position' for this direction is ignored.
<span class=issue>Or is the space at the edge the same as between the
images? Is there no space at the edge?</span> If the image is too big to
fit, one image is placed in the center and clipped.
<dt><dfn id=round>round</dfn>
<dd> The image is repeated as often as it will fit. If it doesn't fit a
whole number of times, it is reduced in size until it does. See
explanation under 'background-size'.
</dl>
<p>Unless one of the two keywords is ''no-repeat'', the whole background
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 'repeat-y': 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 'space': the image of a dot is tiled to
cover the whole background and the images are equally spaced.
</div>
</div>
<h3 id=the-background-attachment><span class=secno>4.4. </span>The
'background-attachment' property</h3>
<table class=propdef id=name-2>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-attachment>background-attachment</dfn>
<tr>
<th>Value:
<td><dfn id=scroll>scroll</dfn> | <dfn id=fixed>fixed</dfn> | <dfn
id=local>local</dfn> [, 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> (
''fixed'') or scroll along with the element ( ''scroll'' and ''local'').
<p>See the section <a href="#layering">“Layering multiple background
images”</a> for how each comma-separated value is applied to each
image of the 'background-image' property.
<p>The difference between ''scroll'' and ''local'' is only visible when the
element has a scrolling mechanism (see 'overflow'): in the case of
''scroll'', 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
''local'', 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.
<p>Even if the image is fixed, it is still only visible when it is in the
content, padding, or border area of the element. Thus, unless the image is
tiled, it may be invisible.
<div class=example>
<p style=display:none>Example(s):
<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 ''fixed'' backgrounds (for example due
to limitations of the hardware platform) should ignore declarations with
the keyword 'fixed'. 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>
<h3 id=the-background-position><span class=secno>4.5. </span>The
'background-position' 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 element's box <em>minus</em> size of background
image; see text
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>for <length> the absolute value, otherwise a percentage
</table>
<p>If background images have been specified, this property specifies their
initial position. The section <a href="#layering">“Layering multiple
background images”</a> defines to which image of 'background-image'
each of the comma-separated values applies.
<p>The <dfn id=ltbg-positiongt><var><bg-position></var></dfn> stands
for: [ [ <var><a href="#ltpercentagegt0"><percentage></a></var> |
<var><a href="#ltlengthgt0"><length></a></var> | left | center |
right ] [ <var><a href="#ltpercentagegt0"><percentage></a></var> |
<var><a href="#ltlengthgt0"><length></a></var> | top | center |
bottom ]? ] | [ [ left | center | right ] || [ top | center | bottom ] ]
<p id=bg-area-edge>Each <var><a
href="#ltbg-positiongt"><bg-position></a></var> specifies an offset
from the top left corner of either the viewport (if<
A0B2
/div>
'background-attachment' is ''fixed'' for this image) or the box given by
'background-origin' (if 'background-attachment' is not ''fixed'').
<p>If only one percentage or length value is given, it sets the horizontal
offset only, and the vertical offset will be 50%. If two values are given,
the horizontal offset comes first. Combinations of keyword, length and
percentage values are allowed, (e.g., ''50% 2cm'' or ''center 2cm'' or
''center 10%''). For pairs of keyword and non-keyword values, 'left' and
'right' may only be used as the first value, and 'top' and 'bottom' may
only be used as the second value. Negative positions are allowed.
<p>The keywords are equivalent to percentages, as follows:
<dl>
<dt>top left,
<dt>left top
<dd> Same as ''0% 0%''.
<dt>top,
<dt>top center,
<dt>center top
<dd> Same as ''50% 0%''.
<dt>right top,
<dt>top right
<dd> Same as ''100% 0%''.
<dt>left,
<dt>left center,
<dt>center left
<dd> Same as ''0% 50%''.
<dt>center,
<dt>center center
<dd> Same as ''50% 50%''.
<dt>right,
<dt>right center,
<dt>center right
<dd> Same as ''100% 50%''.
<dt>bottom left,
<dt>left bottom
<dd> Same as ''0% 100%''.
<dt>bottom,
<dt>bottom center,
<dt>center bottom
<dd> Same as ''50% 100%''.
<dt>bottom right,
<dt>right bottom
<dd> Same as ''100% 100%''.
</dl>
<p>A percentage for the horizontal offset is relative to (<var>width of
element</var> - <var>width of background image</var>). A percentage for
the vertical offset is relative to (<var>height of element</var> -
<var>height of background image</var>), where the size of the image is the
size given by 'background-size' and the size of the element is the size of
the box given by 'background-origin'.
<p>If the element is rendered as multiple boxes (e.g., inline boxes on
several lines, boxes on several pages), the 'background-break' property
determines which box(es) to use.
<div class=example>
<p>For example, with a value pair of ''0% 0%'', the upper left corner of
the image is aligned with the upper left corner of, usually, the box's
<em>padding edge</em>. A value pair of ''100% 100%'' places the lower
right corner of the image in the lower right corner of the area. With a
value pair of ''14% 84%'', the point 14% across and 84% down the image is
to be placed at the point 14% across and 84% down the area.
</div>
<div class=example>
<p style=display:none>Example:
<pre>
body { background: url("banner.jpeg") right top } /* 100% 0% */
body { background: url("banner.jpeg") top center } /* 50% 0% */
body { background: url("banner.jpeg") center } /* 50% 50% */
body { background: url("banner.jpeg") bottom } /* 50% 100% */
</pre>
</div>
<div class=example>
<p style=display:none>Example:
<pre>
body {
background-image: url("logo.png");
background-attachment: fixed;
background-position: 100% 100%;
background-repeat: no-repeat;
}
</pre>
<p>In the example above, the (single) image is placed in the lower-right
corner of the viewport.
</div>
<div class=figure>
<p><img alt="Diagram of image position within element" src=bg-pos.png>
<p class=caption>Diagram of the meaning of 'background-position: 75% 50%'.
</div>
<p class=issue>Anne van Kesteren gave a <a
href="http://lists.w3.org/Archives/Public/www-style/2004Aug/0185">use
case</a> for splitting the property into 'background-position-x' and
'background-position-y'. The use case is to have a single background image
with several columns and rows of slightly different tiles and move it up
or down to the correct tile on each :hover or :active. Only the
y-coordinate changes. [My opinion: it's a rare case and repeating the
x-coordinate three times isn't that onerous. BB]
<p class=issue>Anne van Kesteren also asked for a way to place an image a
fixed distance from the right or bottom edge. This could be done, e.g.,
with expr essions: 'expr(100% - 10px)' or extra keywords: '10px 10px
from-top-right' or '10px/top 10px/right'.
<p class=issue id=bg-inset-rect><a
href="mailto:lightsolphoenix@gmail.com">Kelly Miller</a> suggested <a
href="http://lists.w3.org/Archives/Public/www-style/2005Aug/0030.html"> on
www-style</a> to use 'rect()' and 'inset-rect()' notations instead of
positions. Images are placed in the top left corner of that rectangle and
if they are tiled, they are tiled only within that rectangle. Example:
'background: url(tl) no-repeat, url(middle) inset-rect(20px, 20px, 20px,
20px) space' puts a single “tl” image in the top left and
tiles the “middle” image, but leaves 20px on each side
untiled. Questions: are images clipped to the given rectangle? If so, how
about removing 'background-clip' and allowing 'inset-rect(padding)'?
<h3 id=the-background-clip><span class=secno>4.6. </span>The
'background-clip' property</h3>
<table class=propdef id=name-4>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-clip>background-clip</dfn>
<tr>
<th>Value:
<td>[<dfn id=border0 title=clip-padding>border</dfn> | <dfn id=padding
title=clip-border>padding</dfn>] [, [border | padding]]*
<tr>
<th>Initial: