forked from w3c/csswg-drafts
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathOverview.html
More file actions
5985 lines (4413 loc) · 196 KB
/
Copy pathOverview.html
File metadata and controls
5985 lines (4413 loc) · 196 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 profile="http://dublincore.org/documents/2008/08/04/dc-html/ ">
<meta content="text/html; charset=utf-8" http-equiv=content-type>
<title>CSS Backgrounds and Borders Module Level 3</title>
<link href="http://purl.org/dc/terms/" rel=schema.dcterms>
<link href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=dcterms.rights>
<meta content="CSS Backgrounds and Borders Module Level 3"
name=dcterms.title>
<meta content=text name=dcterms.type>
<meta content=2014-08-13 name=dcterms.date>
<meta content="Bert Bos" name=dcterms.creator>
<meta content="Elika J. Etemad" name=dcterms.creator>
<meta content="Brad Kemper" name=dcterms.creator>
<meta content=W3C name=dcterms.publisher>
<meta content="http://dev.w3.org/csswg/css3-background/"
name=dcterms.identifier>
<link href="#contents" rel=contents>
<link href="#index" rel=index>
<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; }
pre { text-align: left; }
#box-shadow-samples td { background: white; color: black; }
.css::before, .css::after, .property::before, .property::after { content: none !important;}
</style>
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<script defer=defer
src="http://test.csswg.org/harness/annotate.js#css-backgrounds-3_dev"
type="text/javascript"></script>
<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">Editor's Draft 13 August 2014</h2>
<dl>
<dt>This version:
<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>Latest editor's draft:
<dd><a
href="http://dev.w3.org/csswg/css3-background/">http://dev.w3.org/csswg/css3-background/</a>
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2014/WD-css3-background-20140116/">http://www.w3.org/TR/2014/WD-css3-background-20140116/</a>
<dt>Issue Tracking:
<dd><a
href="http://www.w3.org/Style/CSS/Tracker/products/11">http://www.w3.org/Style/CSS/Tracker/products/11</a>
<dt>Feedback:
<dd><a
href="mailto:www-style@w3.org?subject=%5Bcss-backgrounds%5D%20feedback">www-style@w3.org</a>
with subject line “<kbd>[css-backgrounds] <var>… message topic
…</var></kbd>” (<a
href="http://lists.w3.org/Archives/Public/www-style/"
rel=discussion>archives</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>
(Mozilla)
<dd><a href="mailto:brad.kemper@gmail.com">Brad Kemper</a> (Invited
Expert)
<dt>Latest test suite:
<dd><a
href="http://test.csswg.org/suites/css3-background/nightly-unstable/">http://test.csswg.org/suites/css3-background/nightly-unstable/</a>
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2014 <a href="http://www.w3.org/"><abbr
title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><abbr
title="Massachusetts Institute of Technology">MIT</abbr></a>, <a
href="http://www.ercim.eu/"><abbr
title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href="http://www.keio.ac.jp/">Keio</a>, <a
href="http://ev.buaa.edu.cn/">Beihang</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="#ref-CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>, which builds on CSS level 1
<a href="#ref-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?Subject=%5Bcss3-background%5D%20PUT%20SUBJECT%20HERE">
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>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 implementers:
animatability of ‘<a href="#box-shadow"><code
class=property>box-shadow</code></a>’
<p>The CSS WG maintains an <a
href="http://www.w3.org/Style/CSS/Tracker/products/11">issues list</a> for
this module. A <a href="http://www.w3.org/Style/CSS/Test/">test suite</a>
and implementation report for CSS Backgrounds and Borders Level 3 will be
developed during the Candidate Recommendation phase, which will last a
minimum of three months, and at least until 25 July 2012. See the section
<a href="#exit">“CR exit criteria”</a> for more details.
<p>The changes to this specification since the previous drafts are listed
in the <a href="#changes">“Changes”</a> section.
<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 and
Interactions</a>
<ul class=toc>
<li><a href="#placement"><span class=secno>2.1. </span> Module
Interactions</a>
<li><a href="#value-types"><span class=secno>2.2. </span> Value
Types</a>
<li><a href="#animations"><span class=secno>2.3. </span>Animated
Values</a>
</ul>
<li><a href="#backgrounds"><span class=secno>3. </span> Backgrounds</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>Base
Color: the ‘<code class=property>background-color</code>’
property</a>
<li><a href="#the-background-image"><span class=secno>3.3. </span>Image
Sources: the ‘<code class=property>background-image</code>’
property</a>
<li><a href="#the-background-repeat"><span class=secno>3.4.
</span>Tiling Images: the ‘<code
class=property>background-repeat</code>’ property</a>
<li><a href="#the-background-attachment"><span class=secno>3.5.
</span>Affixing Images: the ‘<code
class=property>background-attachment</code>’ property</a>
<li><a href="#the-background-position"><span class=secno>3.6.
</span>Positioning Images: the ‘<code
class=property>background-position</code>’ property</a>
<li><a href="#the-background-clip"><span class=secno>3.7.
</span>Painting Area: the ‘<code
class=property>background-clip</code>’ property</a>
<li><a href="#the-background-origin"><span class=secno>3.8.
</span>Positioning Area: the ‘<code
class=property>background-origin</code>’ property</a>
<li><a href="#the-background-size"><span class=secno>3.9. </span>Sizing
Images: the ‘<code class=property>background-size</code>’
property</a>
<li><a href="#the-background"><span class=secno>3.10. </span>Backgrounds
Shorthand: the ‘<code class=property>background</code>’
property</a>
<li><a href="#special-backgrounds"><span class=secno>3.11. </span>
Backgrounds of Special Elements</a>
</ul>
<li><a href="#borders"><span class=secno>4. </span> Borders</a>
<ul class=toc>
<li><a href="#the-border-color"><span class=secno>4.1. </span>Line
Colors: the ‘<code class=property>border-color</code>’
properties</a>
<li><a href="#the-border-style"><span class=secno>4.2. </span>Line
Patterns: the ‘<code class=property>border-style</code>’
properties</a>
<li><a href="#the-border-width"><span class=secno>4.3. </span>Line
Thickness: the ‘<code class=property>border-width</code>’
properties</a>
<li><a href="#the-border-shorthands"><span class=secno>4.4.
</span>Border Shorthand Properties</a>
</ul>
<li><a href="#corners"><span class=secno>5. </span>Rounded Corners</a>
<ul class=toc>
<li><a href="#the-border-radius"><span class=secno>5.1. </span>Curve
Radii: the ‘<code class=property>border-radius</code>’
properties</a>
<li><a href="#corner-shaping"><span class=secno>5.2. </span>Corner
Shaping</a>
<li><a href="#corner-clipping"><span class=secno>5.3. </span>Corner
Clipping</a>
<li><a href="#corner-transitions"><span class=secno>5.4. </span>Color
and Style Transitions</a>
<li><a href="#corner-overlap"><span class=secno>5.5. </span>Overlapping
Curves</a>
<li><a href="#border-radius-tables"><span class=secno>5.6. </span>Effect
on Tables</a>
</ul>
<li><a href="#border-images"><span class=secno>6. </span>Border Images</a>
<ul class=toc>
<li><a href="#the-border-image-source"><span class=secno>6.1.
</span>Image Source: the ‘<code
class=property>border-image-source</code>’ property</a>
<li><a href="#the-border-image-slice"><span class=secno>6.2.
</span>Image Slicing: the ‘<code
class=property>border-image-slice</code>’ property</a>
<li><a href="#the-border-image-width"><span class=secno>6.3.
</span>Drawing Areas: the ‘<code
class=property>border-image-width</code>’ property</a>
<li><a href="#the-border-image-outset"><span class=secno>6.4.
</span>Edge Overhang: the ‘<code
class=property>border-image-outset</code>’ property</a>
<li><a href="#the-border-image-repeat"><span class=secno>6.5.
</span>Image Tiling: the ‘<code
class=property>border-image-repeat</code>’ property</a>
<li><a href="#border-image-process"><span class=secno>6.6. </span>
Drawing the Border Image</a>
<li><a href="#the-border-image"><span class=secno>6.7. </span>Border
Image Shorthand: the ‘<code class=property>border-image</code>’
property</a>
<li><a href="#border-image-tables"><span class=secno>6.8. </span>Effect
on Tables</a>
</ul>
<li><a href="#misc"><span class=secno>7. </span>Miscellaneous Effects</a>
<ul class=toc>
<li><a href="#the-box-shadow"><span class=secno>7.1. </span>Drop
Shadows: the ‘<code class=property>box-shadow</code>’ property</a>
<ul class=toc>
<li><a href="#shadow-shape"><span class=secno>7.1.1. </span> Shadow
Shape, Spread, and Knockout</a>
<li><a href="#shadow-blur"><span class=secno>7.1.2. </span> Blurring
Shadow Edges</a>
<li><a href="#shadow-layers"><span class=secno>7.1.3. </span>
Layering, Layout, and Other Details</a>
</ul>
</ul>
<li><a href="#definitions"><span class=secno>8. </span>Definitions</a>
<ul class=toc>
<li><a href="#glossary"><span class=secno>8.1. </span>Glossary</a>
<li><a href="#conformance"><span class=secno>8.2. </span>Conformance</a>
<li><a href="#levels"><span class=secno>8.3. </span>Levels</a>
<ul class=toc>
<li><a href="#level-1"><span class=secno>8.3.1. </span>Level 1</a>
<li><a href="#level-2"><span class=secno>8.3.2. </span>Level 2</a>
<li><a href="#level-3"><span class=secno>8.3.3. </span>Level 3</a>
</ul>
<li><a href="#exit"><span class=secno>8.4. </span> CR Exit Criteria</a>
</ul>
<li><a href="#changes"><span class=secno>9. </span> Changes</a>
<ul class=toc>
<li><a href="#changes-2012-07"><span class=secno>9.1. </span> Changes
since the 24 July 2012 Candidate Recommendation</a>
<li><a href="#changes-2012-04"><span class=secno>9.2. </span> Changes
since the 17 April 2012 Candidate Recommendation</a>
<li><a href="#changes-2012LC"><span class=secno>9.3. </span> Changes
since the 14 February 2012 “Last Call” Working Draft</a>
<li><a href="#changes-2011"><span class=secno>9.4. </span> Changes Since
the 15 February 2011 Candidate Recommendation</a>
<li><a href="#changes-2009"><span class=secno>9.5. </span> Changes Since
the 17 December 2009 Candidate Recommendation</a>
</ul>
<li><a href="#acknowledgments"><span class=secno>10.
</span>Acknowledgments</a>
<li><a href="#references"><span class=secno>11. </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 subsection 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="#ref-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="#ref-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 ‘<a
href="#box-shadow"><code class=property>box-shadow</code></a>’ property.
<p>If an element is broken into multiple boxes, ‘<code
class=property>box-decoration-break</code>’ <a href="#ref-CSS3-BREAK"
rel=biblioentry>[CSS3-BREAK]<!--{{CSS3-BREAK}}--></a> defines 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="#ref-CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
<h2 id=values><span class=secno>2. </span> Values and Interactions</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="#ref-CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
<h3 id=placement><span class=secno>2.1. </span> Module Interactions</h3>
<p>This module replaces and extends the background and border features
defined in <a href="#ref-CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> sections 8.5 and 14.2.
<p>All properties in this module apply to the <a
href="http://www.w3.org/TR/CSS21/selector.html#first-letter"><code>::first-letter</code></a>
pseudo-element. The <a href="#backgrounds">background properties</a> and
<a href="#corners">border-radius properties</a> also apply to the <a
href="http://www.w3.org/TR/CSS21/selector.html#first-line-pseudo"><code>::first-line</code></a>
pseudo-element. The UA may (but is not required to) apply the <a
href="#border-images">border-image</a> or ‘<a href="#box-shadow"><code
class=property>box-shadow</code></a>’ properties to
<code>::first-line</code>. The UA must not apply the <a
href="#borders">border-color/style/width properties</a> to
<code>::first-line</code>. <a href="#ref-CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>
<h3 id=value-types><span class=secno>2.2. </span> Value Types</h3>
<p>The <dfn id=ltimagegt><var><image></var></dfn> value type is
defined by this specification as <code class=prod><a
href="#ltimagegt"><var><image></var></a> =
<var><uri></var></code>. Other value types are defined in CSS
Level 2 Revision 1 <a href="#ref-CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. Other CSS modules may expand
the definitions of these value types: for example <a href="#ref-CSS3COLOR"
rel=biblioentry>[CSS3COLOR]<!--{{CSS3COLOR}}--></a>, when combined with
this module, expands the definition of the <color> value type as
used in this specification. Similarly, <a href="#ref-CSS3-IMAGES"
rel=biblioentry>[CSS3-IMAGES]<!--{{CSS3-IMAGES}}--></a>, when combined
with this module, expands the definition of <a
href="#ltimagegt"><var><image></var></a> as used in this
specification.
<p>In addition to the property-specific values listed in their definitions,
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 property value. For readability it has not been repeated
explicitly.
<h3 id=animations><span class=secno>2.3. </span>Animated Values</h3>
<p><!-- <a href="http://www.w3.org/Style/CSS/Tracker/issues/210"
>ISSUE-210.]</a> -->
It is expected that CSS will include ways to animate transitions between
styles. (The section <a
href="http://www.w3.org/TR/css3-transitions/#animatable-types">“Animation
of property types”</a> of the <cite>CSS Transitions module</cite> <a
href="#ref-CSS3-TRANSITIONS"
rel=biblioentry>[CSS3-TRANSITIONS]<!--{{CSS3-TRANSITIONS}}--></a> is
expected to define how different kinds of values are interpolated during a
transition.) In anticipation of that, this module includes a line
“Animatable” for each property, which specifies whether and how values
of the property can be animated.
<h2 id=backgrounds><span class=secno>3. </span> Backgrounds</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 (‘<a href="#background-color"><code
class=property>background-color</code></a>’) and images (‘<a
href="#background-image"><code
class=property>background-image</code></a>’) 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 ‘<a
href="#background-color"><code
class=property>background-color</code></a>’.
<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 ‘<a
href="#background-image"><code
class=property>background-image</code></a>’ 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 ‘<a href="#background-origin"><code
class=property>background-origin</code></a>’ and ‘<a
href="#background-repeat"><code
class=property>background-repeat</code></a>’ 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>Base Color: the
‘<a href="#background-color"><code
class=property>background-color</code></a>’ property</h3>
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-color>background-color</dfn>
<tr>
<th><a href="#values">Value</a>:
<td><var><color></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
<tr>
<th>Animatable:
<td>as <a
href="http://www.w3.org/TR/css3-transitions/#animtype-color">color</a>
</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 ‘<a
href="#background-clip"><code class=property>background-clip</code></a>’
value associated with the bottom-most background image layer.
<h3 id=the-background-image><span class=secno>3.3. </span>Image Sources:
the ‘<a href="#background-image"><code
class=property>background-image</code></a>’ property</h3>
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-image>background-image</dfn>
<tr>
<th><a href="#values">Value</a>:
<td><a href="#ltbg-imagegt"><var><bg-image></var></a> [ , <a
href="#ltbg-imagegt"><var><bg-image></var></a> ]*
<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
<tr>
<th>Animatable:
<td>no
</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> = <a
href="#ltimagegt"><var><image></var></a> | none</pre>
<p>A value of <dfn id=none
title="''none''!!'background-image' value">‘<code
class=css>none</code>’</dfn> 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 ‘<a href="#background-image"><code
class=property>background-image</code></a>’ interacts with other
comma-separated background properties to form each background image layer.
<p>When setting a background image, authors should also specify a ‘<a
href="#background-color"><code class=css>background-color</code></a>’
that will preserve contrast with the text for when the image is
unavailable.
<p>For accessibility reasons, authors should not use background images as
the sole method of conveying important information. See <a
href="http://www.w3.org/TR/2008/NOTE-WCAG20-TECHS-20081211/F3">Web Content
Accessibility Guideline F3</a> <a href="#ref-WCAG20"
rel=biblioentry>[WCAG20]<!--{{WCAG20}}--></a>. Images are not accessible
in non-graphical presentations, and background images specifically might
be turned off in high-contrast display modes.
<p class=note>Note that stylistic foreground images can be provided in CSS
with the <a
href="http://www.w3.org/TR/CSS21/generate.html#content">content</a>
property. (Semantically-important foreground images should be provided in
the document markup, e.g. with the <img> tag in HTML.)
<p class=note><a
href="http://www.w3.org/TR/media-frags/#naming-space">Media fragments</a>
can be used to display a portion of an image. The <a
href="http://www.w3.org/TR/css3-images/">CSS Images</a> module will
provide fallback syntax for image formats and include additional controls
for image display.
<div class=example>
<p>Some examples specifying background images:
<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>Tiling Images:
the ‘<a href="#background-repeat"><code
class=property>background-repeat</code></a>’ property</h3>
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-repeat>background-repeat</dfn>
<tr>
<th><a href="#values">Value</a>:
<td><a href="#ltrepeat-stylegt"><var><repeat-style></var></a> [ ,
<a href="#ltrepeat-stylegt"><var><repeat-style></var></a> ]*
<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>A list, each item consisting of: two keywords, one per dimension
<tr>
<th>Animatable:
<td>no
</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=ltrepeat-stylegt><var><repeat-style></var></dfn> = repeat-x | repeat-y | [repeat | space | round | no-repeat]{1,2}</pre>
<p>Single values for <a
href="#ltrepeat-stylegt"><var><repeat-style></var></a> have the
following meanings:
<dl>
<dt><dfn id=repeat-x>‘<code class=css>repeat-x</code>’</dfn>
<dd> Computes to ‘<code class=css>repeat no-repeat</code>’.
<dt><dfn id=repeat-y>‘<code class=css>repeat-y</code>’</dfn>
<dd> Computes to ‘<code class=css>no-repeat repeat</code>’.
<dt>‘<code class=css>repeat</code>’
<dd> Computes to ‘<code class=css>repeat repeat</code>’.
<dt>‘<code class=css>space</code>’
<dd> Computes to ‘<code class=css>space space</code>’
<dt>‘<code class=css>round</code>’
<dd> Computes to ‘<code class=css>round round</code>’
<dt>‘<code class=css>no-repeat</code>’
<dd> Computes to ‘<code class=css>no-repeat no-repeat</code>’
</dl>
<p>If a <a href="#ltrepeat-stylegt"><var><repeat-style></var></a>
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 title="''repeat''!!'background-repeat' value">‘<code
class=css>repeat</code>’</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-area0>background painting area</a>.
<dt><dfn id=space title="''space''!!'background-repeat' value">‘<code
class=css>space</code>’</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 <a class=index
href="#background-painting-area" id=background-painting-area1>background
painting area</a> is larger than the background positioning area, then
the pattern repeats to fill the background painting area. The value of
‘<a href="#background-position"><code
class=property>background-position</code></a>’ 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 ‘<a
href="#background-position"><code
class=property>background-position</code></a>’ determines its position
in this direction.
<dt><dfn id=round title="''round''!!'background-repeat' value">‘<code
class=css>round</code>’</dfn>
<dd> The image is repeated as often as will fit within the <a class=index
href="#background-positioning-area"
id=background-positioning-area.>background positioning area.</a> If it
doesn't fit a whole number of times, it is rescaled so that it does. See
the formula under ‘<a href="#background-size"><code
class=property>background-size</code></a>’. If the <a class=index
href="#background-painting-area" id=background-painting-area2>background
painting area</a> is larger than the background positioning area, then
the pattern repeats to fill the background painting area.
<dt><dfn id=no-repeat
title="''no-repeat''!!'background-repeat' value">‘<code
class=css>no-repeat</code>’</dfn>
<dd> The image is placed once and not repeated in this direction.
</dl>
<p>Unless one of the two keywords is ‘<code
class=css>no-repeat</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 ‘<a href="#repeat-y"><code
class=css>repeat-y</code></a>’: 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>space</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 ‘<a href="#background-repeat"><code
class=property>background-repeat</code></a>’ interacts with other
comma-separated background properties to form each background image layer.
<h3 id=the-background-attachment><span class=secno>3.5. </span>Affixing
Images: the ‘<a href="#background-attachment"><code
class=property>background-attachment</code></a>’ property</h3>
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=background-attachment>background-attachment</dfn>
<tr>
<th><a href="#values">Value</a>:
<td><a href="#ltattachmentgt"><var><attachment></var></a> [ , <a
href="#ltattachmentgt"><var><attachment></var></a> ]*
<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
<tr>
<th>Animatable:
<td>no
</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>
(<dfn id=fixed>‘<code class=css>fixed</code>’</dfn>) or scroll along
with the element (<dfn id=scroll>‘<code
class=css>scroll</code>’</dfn>) or its contents (<dfn id=local>‘<code
class=css>local</code>’</dfn>). The property's value is given as a
comma-separated list of <attachment> keywords where
<pre class=prod><dfn