-
Notifications
You must be signed in to change notification settings - Fork 790
Expand file tree
/
Copy pathOverview.html
More file actions
4951 lines (3618 loc) · 157 KB
/
Overview.html
File metadata and controls
4951 lines (3618 loc) · 157 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!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">
.prod { font-family: inherit; font-size: inherit }
pre.prod { white-space: pre-wrap; margin: 1em 0 1em 2em }
code { font-size: inherit; }
#box-shadow-samples td { background: white; color: black; }
</style>
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.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>CSS Backgrounds and Borders Module Level 3</h1>
<h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 31 July 2009</h2>
<dl>
<dt>This version:
<dd><!-- <a href="http://www.w3.org/TR/2009/WD-css3-background-20090731">http://www.w3.org/TR/2009/WD-css3-background-20090731</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>
(Invited Expert)
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2009 <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 <a
href="#document">documents</a> (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. Its publication here does
not imply endorsement of its contents by W3C. Don't cite this document
other than as 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="/Style/CSS/members">CSS
Working Group</a> (part of the <a href="/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
Policy</a>. W3C maintains a <a href="/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="/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
W3C Patent Policy</a>.</p>
<!--end-status-->
<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. <strong>If there's a conflict between CSS Backgrounds and
Borders Level 3 and CSS 2.1, please report it to the CSS Working Group.
Since these specs are intended to be consistent with each other, conflicts
indicate an error in one or both specs.</strong>
<p>The following features are at-risk and may be dropped at the end of the
CR period if there has not been enough interest from implementors: inner
shadows for ‘<code class=property><a
href="#box-shadow">box-shadow</a></code>’, ‘<code
class=property><a href="#border-break">border-break</a></code>’,
‘<code class=property><a
href="#background-break">background-break</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="#backgrounds"><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"><span class=secno>3.10 </span>The
‘<code class=property>background</code>’ shorthand
property</a>
<li><a href="#special-backgrounds"><span class=secno>3.11 </span>The
backgrounds of special elements</a>
</ul>
<li><a href="#borders"><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-radius"><span class=secno>4.4 </span>The
‘<code class=property>border-radius</code>’ properties</a>
<li><a href="#the-border-shorthands"><span class=secno>4.5 </span>The
border shorthand properties</a>
</ul>
<li><a href="#border-images"><span class=secno>5 </span>Border Images</a>
<ul class=toc>
<li><a href="#the-border-image-source"><span class=secno>5.1 </span>The
‘<code class=property>border-image-source</code>’
property</a>
<li><a href="#the-border-image-slice"><span class=secno>5.2 </span>The
‘<code class=property>border-image-slice</code>’
property</a>
<li><a href="#the-border-image-width"><span class=secno>5.3 </span>The
‘<code class=property>border-image-width</code>’
property</a>
<li><a href="#the-border-image-outset"><span class=secno>5.4 </span>The
‘<code class=property>border-image-outset</code>’
property</a>
<li><a href="#the-border-image-repeat"><span class=secno>5.5 </span>The
‘<code class=property>border-image-repeat</code>’
property</a>
<li><a href="#border-image-process"><span class=secno>5.6
</span>Border-image drawing process</a>
<li><a href="#the-border-image"><span class=secno>5.7 </span>The
‘<code class=property>border-image</code>’ shorthand</a>
</ul>
<li><a href="#misc"><span class=secno>6 </span>Miscellaneous Effects</a>
<ul class=toc>
<li><a href="#the-border-break"><span class=secno>6.1 </span>The
‘<code class=property>border-break</code>’ property</a>
<li><a href="#the-background-break-property"><span class=secno>6.2
</span>The ‘<code class=property>background-break</code>’
property</a>
<li><a href="#the-box-shadow"><span class=secno>6.3 </span>The
‘<code class=property>box-shadow</code>’ property</a>
</ul>
<li><a href="#definitions"><span class=secno>7 </span>Definitions</a>
<ul class=toc>
<li><a href="#glossary"><span class=secno>7.1 </span>Glossary</a>
<li><a href="#conformance"><span class=secno>7.2 </span>Conformance</a>
<li><a href="#levels"><span class=secno>7.3 </span>Levels</a>
<ul class=toc>
<li><a href="#level-1"><span class=secno>7.3.1 </span>CSS Level 1</a>
<li><a href="#level-2"><span class=secno>7.3.2 </span>CSS Level 2</a>
<li><a href="#level-3"><span class=secno>7.3.3 </span>CSS Level 3</a>
</ul>
<li><a href="#exit"><span class=secno>7.4 </span>CR exit criteria</a>
</ul>
<li><a href="#acknowledgments"><span class=secno>8
</span>Acknowledgments</a>
<li><a href="#references"><span class=secno>9 </span>References</a>
<ul class=toc>
<li class=no-num><a href="#normative-references">Normative
references</a>
<li class=no-num><a href="#other-references">Other references</a>
</ul>
<li class=no-num><a href="#property-index">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 properties of this module deal with the decoration of the border
area and with the background of the content, padding and border areas.
Additionally the box may be given a "drop-shadow" effect with the
‘<code class=property><a
href="#box-shadow">box-shadow</a></code>’ property.
<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. (An element can
result in more than one box if it is broken at the end of a line, at the
end of a column or at the end of a page; and continued in the next line,
column or page.)
<p>The relative stacking order of backgrounds, borders, and shadows is
given in this module. For how these layers interact with other rendered
content, see Appendix E “Elaborate description of Stacking Contexts”
in <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
<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><dfn id=ltcolorgt><var><color></var></dfn> values are defined in
CSS Color Level 3 <a href="#CSS3COLOR"
rel=biblioentry>[CSS3COLOR]<!--{{!CSS3COLOR}}--></a>.
<p><dfn id=ltimagegt><var><image></var></dfn> values are defined by
this specification as <code class=prod><var><a
href="#ltimagegt"><image></a></var> = <var><uri></var></code>.
<p class=note>A future specification may expand the definition of <var><a
href="#ltimagegt"><image></a></var> 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>.
<p>All properties defined in this specification also accept the <a
href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">inherit</a>
keyword as their value, but for readability it has not been listed
explicitly.
<h2 id=backgrounds><span class=secno>3 </span>Background properties</h2>
<p>Each box has a background layer that may be fully transparent (the
default), or filled with a color and/or one or more images. 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, and
how they are sized, positioned, tiled, etc.
<p>The background properties are not inherited, but the parent box's
background will shine through by default because of the initial
‘<code class=property>transparent</code>’ value on
‘<code class=property><a
href="#background-color">background-color</a></code>’.
<h3 id=layering><span class=secno>3.1 </span>Layering multiple background
images</h3>
<p>The background of a box can have multiple <span class=index
id=layers>layers</span> in CSS3. The number of layers is determined by the
number of comma-separated values in the ‘<code class=property><a
href="#background-image">background-image</a></code>’ property. Note
that a value of ‘<code class=property>none</code>’ still
creates a layer.
<p>Each of the images is sized, positioned, and tiled according to the
corresponding value in the other background properties. The lists are
matched up from the first value: excess values at the end are not used. If
a property doesn't have enough comma-separated values to match the number
of layers, the <a href="#ua">UA</a> must calculate its used value by
repeating the list of values until there are enough.
<div class=example>
<p>For example, this set of declarations:
<pre>
background-image: url(flower.png), url(ball.png), url(grass.png);
background-position: center center, 20% 80%, top left, bottom right;
background-origin: border-box, content-box;
background-repeat: no-repeat;
</pre>
<p>has exactly the same effect as this set with the extra position dropped
and the missing values for ‘<code class=property><a
href="#background-origin">background-origin</a></code>’ and
‘<code class=property><a
href="#background-repeat">background-repeat</a></code>’ filled in
(emphasized 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<strong>, border-box</strong>;
background-repeat: no-repeat<strong>, no-repeat, no-repeat</strong>;
</pre>
</div>
<p>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.
<p class=note>Note that the <a href="#border-images">border-image
properties</a> can also define a background image, which, if present, is
painted on top of the background created by the background properties.
<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>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-color>background-color</dfn>
<tr>
<th>Value:
<td><var><a href="#ltcolorgt"><color></a></var>
<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 <span class=index id=background-color0
title="color!!background">background color</span> of an element. The color
is drawn behind any background images.
<div class=example>
<p>Example:
<pre>h1 { background-color: #F00 } /* Sets background to red. */</pre>
</div>
<p>The background color is 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>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-image>background-image</dfn>
<tr>
<th>Value:
<td><var><a href="#ltbg-imagegt"><bg-image></a></var> [ , <var><a
href="#ltbg-imagegt"><bg-image></a></var> ]*
<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. Where
<pre
class=prod><dfn id=ltbg-imagegt><var><bg-image></var></dfn> = <var><a href="#ltimagegt"><image></a></var> | none</pre>
<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) likewise counts as a layer
but draws nothing.
<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.
<p>When setting a background image, authors should also specify a
‘<code class=css><a
href="#background-color">background-color</a></code>’ that will
preserve contrast with the text for when the image is unavailable.
<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>
<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 <a
href="#the-background-size">sized</a> and <a
href="#the-background-position">positioned</a>. Where
<pre
class=prod><dfn id=ltrepeatgt><var><repeat></var></dfn> = 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:
<dl>
<dt><dfn id=repeat>repeat</dfn>
<dd> The image is repeated in this direction as often as needed to cover
the <a class=index href="#background-painting-area"
id=background-painting-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 class=index
href="#background-positioning-area"
id=background-positioning-area0>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></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="#background-positioning-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>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-attachment>background-attachment</dfn>
<tr>
<th>Value:
<td><var><a href="#ltattachmentgt"><attachment></a></var> [ ,
<var><a href="#ltattachmentgt"><attachment></a></var> ]*
<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>’). Where
<pre
class=prod><dfn id=ltattachmentgt><var><attachment></var></dfn> = scroll | fixed | local</pre>
<p>Note that there is only one viewport per view. If an element has a
scrolling mechanism (see the ‘<code
class=property>overflow</code>’ property <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>), a ‘<code
class=css>fixed</code>’ background doesn't move with the element,
and a ‘<code class=css>scroll</code>’ background doesn't move
with the scrolling mechanism.
<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: 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, effectively.)
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="#border-box">border-box</a></code>’ value 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>In paged media where there is no viewport, a ‘<code
class=css>fixed</code>’ background is fixed with respect to the <a
href="http://www.w3.org/TR/CSS21/page.html#page-box">page box</a>.
<p>Even if the image is fixed, it is still only visible when it is in the
<em><a href="#background-painting-area">background painting area</a></em>
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>
<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 <a class=index href="#background-positioning-area"
id=background-positioning-area1>background positioning area</a>
<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 (after any <a href="#the-background-size">resizing</a>)
within their corresponding <a
href="#background-positioning-area">background positioning area.</a>
<p>Where
<pre
class=prod><dfn id=ltbg-positiongt><var><bg-position></var></dfn> = [
[ [ <var><percentage></var> | <var><length></var> | left | center | right ] ]
[ [ <var><percentage></var> | <var><length></var> | top | center | bottom ] ]?
|
[ center | [ left | right ] [ <var><percentage></var> | <var><length></var> ]? ] ||
[ center | [ top | bottom ] [ <var><percentage></var> | <var><length></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.
<div class=example>
<p>The following declarations give the stated (horizontal, vertical)
offsets from the top left corner:</p>
<pre>
background-position: left 10px top 15px; /* 10px, 15px */
background-position: left top ; /* 0px, 0px */
background-position: 10px 15px; /* 10px, 15px */
background-position: left 15px; /* 0px, 15px */
background-position: 10px top ; /* 10px, 0px */
background-position: left top 15px; /* 0px, 15px */
background-position: left 10px top ; /* 10px, 0px */</pre>
</div>
<dl>
<dt><percentage>
<dd>
<p>A percentage for the horizontal offset is relative to (<var>width