-
Notifications
You must be signed in to change notification settings - Fork 792
Expand file tree
/
Copy pathOverview.bs
More file actions
2886 lines (2360 loc) · 104 KB
/
Overview.bs
File metadata and controls
2886 lines (2360 loc) · 104 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
<!--
Coding style convention in this file:
* Use semantic line breaks (http://rhodesmill.org/brandon/2012/one-sentence-per-line/)
* Tabs for indentation, spaces for allignment (http://lea.verou.me/2012/01/why-tabs-are-clearly-superior/)
* Use markdown paragraphs (empty lines between paragraphs) over <p> when practical
* two empty lines above <h*>, one below <h*>, one between <hn> and <hn+1>
* empty line between <ol>, <ul>, <table>, <div> and ajacent text
* Don't close <p>, <li>, <dd>, <dt>, <tr>, <th>, or <td>
* Indent the content and break line after the opening <li>, <dd>, <dt>, <td>, or <th> if it's more than 2 lines long
or for lists where at least some elements are more than 2 lines long
* Empty line between adjacent <li>, <th>, <td>, <tr>, and between <dd> and the next <dt>;
Can be skipped if all items are very short
* Indent the content of <ol>, <ul>, <dl>, <table>, <tr>
* Indent the content of <div class=note> and <div class=example>
-->
<pre class="anchors">
spec: css2; urlPrefix: https://drafts.csswg.org/css2/
urlPrefix: box.html
type: dfn;
text: content edge;
text: padding edge;
</pre>
<pre class='metadata'>
Title: CSS Basic User Interface Module Level 4
ED: https://drafts.csswg.org/css-ui-4/
Status Text: This specification will include and extend <cite>CSS Basic User Interface Module Level 3.</cite> [[CSS-UI-3]]
TR: https://www.w3.org/TR/css-ui-4/
Previous Version: https://www.w3.org/TR/2017/WD-css-ui-4-20171222/
Previous Version: https://www.w3.org/TR/2015/WD-css-ui-4-20150922/
Shortname: css-ui
Level: 4
Group: csswg
Status: ED
Work Status: Revising
Editor: Florian Rivoal, On behalf of Bloomberg, https://florian.rivoal.net/, w3cid 43241
Abstract: This specification describes user interface related
properties and values to style HTML and XML (including XHTML).
It includes and extends user interface related features
from the properties and values of previous CSS levels.
It uses various properties and values
to style basic user interface elements in a document.
At risk: Applicability of 'user-select' to ''::before'' and ''::after''
Can I Use URL: https://drafts.csswg.org/css-ui-3/
Can I Use URL: http://drafts.csswg.org/css-ui-3/
Can I Use URL: https://drafts.csswg.org/css-ui/
Can I Use URL: http://drafts.csswg.org/css-ui/
Can I Use URL: https://www.w3.org/TR/css-ui-3/
Can I Use URL: http://www.w3.org/TR/css-ui-3/
Can I Use URL: https://www.w3.org/TR/css3-ui/
Can I Use URL: http://www.w3.org/TR/css3-ui/
Can I Use URL: https://drafts.csswg.org/css-ui-4/
Can I Use URL: http://drafts.csswg.org/css-ui-4/
Can I Use URL: https://www.w3.org/TR/css-ui-4/
Can I Use URL: http://www.w3.org/TR/css-ui-4/
Ignore Can I Use URL Failure: https://drafts.csswg.org/css-ui-3/
Ignore Can I Use URL Failure: http://drafts.csswg.org/css-ui-3/
Ignore Can I Use URL Failure: https://drafts.csswg.org/css-ui/
Ignore Can I Use URL Failure: http://drafts.csswg.org/css-ui/
Ignore Can I Use URL Failure: https://www.w3.org/TR/css-ui-3/
Ignore Can I Use URL Failure: http://www.w3.org/TR/css-ui-3/
Ignore Can I Use URL Failure: https://www.w3.org/TR/css3-ui/
Ignore Can I Use URL Failure: http://www.w3.org/TR/css3-ui/
Ignore Can I Use URL Failure: https://drafts.csswg.org/css-ui-4/
Ignore Can I Use URL Failure: http://drafts.csswg.org/css-ui-4/
Ignore Can I Use URL Failure: https://www.w3.org/TR/css-ui-4/
Ignore Can I Use URL Failure: http://www.w3.org/TR/css-ui-4/
</pre>
<pre class=link-defaults>
spec:css-writing-modes-4; type:dfn; text:start
spec:css-writing-modes-4; type:dfn; text:end
spec:css22; type:property; text:min-width
spec:css22; type:property; text:max-width
spec:css22; type:property; text:min-height
spec:css22; type:property; text:max-height
spec:css-pseudo-4; type:selector; text:::before
spec:css-pseudo-4; type:selector; text:::after
spec:css-pseudo-4; type:selector; text:::first-line
spec:css-pseudo-4; type:selector; text:::first-letter
spec:selectors-4; type:selector; text::checked
spec:css-display-3; type:property; text:display
spec:css-color-4; type:value; text:currentcolor
</pre>
<pre class="anchors">
url: https://www.w3.org/TR/CSS21/box.html#border-edge; type: dfn; spec: CSS21; text: border edge
</pre>
<style>
.awesome-table td {padding:5px}
.awesome-table {color:#000;background:#fff;margin: auto;}
</style>
<h2 id="intro">Introduction</h2>
This module describes CSS properties which enable authors
to style user interface related properties and values.
<a href="https://www.w3.org/TR/REC-CSS1#anchor-pseudo-classes">Section 2.1 of CSS1</a> [[CSS1]]
and <a href="https://www.w3.org/TR/CSS2/ui.html">Chapter 18 of CSS2</a> [[CSS21]]
introduced several user interface related properties and values.
<a href="https://www.w3.org/TR/2000/WD-css3-userint-20000216">User Interface for CSS3 (16 February 2000)</a> introduced several new user interface related features.
[[CSS-UI-3]] was later introduced to incorporates, extends, and supersedes these.
This specification continues this work, and in turn replaces [[CSS-UI-3]].
<h3 id="purpose">Purpose</h3>
The purpose of this specification is to achieve the following objectives:
<ul>
<li>Extend the user interface features in [[CSS21]] and [[CSS-UI-3]]
<li>Provide additional CSS mechanisms to augment or replace other
dynamic presentation related features in HTML.
<li>Introduce directional navigation properties to assist in the construction of
user interfaces which make use of a directional navigation model.
</ul>
<h2 id="interaction">Module Interactions</h2>
This document defines new features not present in earlier specifications.
In addition, it replaces and supersedes [[!CSS-UI-3]],
which itself replaced and superseded the following:
<ul>
<li>
<a href="https://www.w3.org/TR/CSS21/ui.html#cursor-props">Section 18.1</a>,
<a href="https://www.w3.org/TR/CSS21/ui.html#dynamic-outlines">section 18.4</a>,
and Information on the stacking of outlines defined in
<a href="https://www.w3.org/TR/CSS21/zindex.html">Appendix E</a>
of Cascading Style Sheets, level 2, revision 1 [[CSS21]]
<li>
<a href="https://www.w3.org/TR/2000/WD-css3-userint-20000216">User Interface for CSS3 (16 February 2000)</a> [[CSS-UI-3]]
</ul>
<h2 id="box-model">Box Model addition</h2>
<h3 id="box-sizing" caniuse="css3-boxsizing">Changing the Box Model: the 'box-sizing' property</h3>
<pre class="propdef">
Name: box-sizing
Value: content-box | border-box
Initial: content-box
Applies to: all elements that accept width or height
Inherited: no
Percentages: N/A
Media: visual
Computed value: specified value
</pre>
<dl dfn-type=value dfn-for=box-sizing>
<dt><dfn>content-box</dfn>
<dd>
This is the behavior of width and height as specified by CSS2.1.
The specified width and height (and respective min/max properties)
apply to the width and height respectively of the content box of the element.
The padding and border of the element are laid out
and drawn outside the specified width and height.
<dt><dfn>border-box</dfn>
<dd>
Length and percentages values for width and height (and respective min/max properties)
on this element determine the border box of the element.
That is, any padding or border specified on the element
is laid out and drawn inside this specified width and height.
The content width and height are calculated
by subtracting the border and padding widths of the respective sides
from the specified 'width'
and 'height' properties.
As the content width and height
<a href="https://www.w3.org/TR/CSS21/visudet.html#the-width-property">cannot be negative</a> ([[!CSS21]], section 10.2),
this computation is floored at 0.
Used values, as exposed for instance through getComputedStyle(), also refer to the border box.
Note: This is the behavior of width and height as commonly implemented
by legacy HTML user agents for replaced elements and input elements.
</dl>
Note: In contrast to the length and percentage values,
the ''width/auto'' value of the 'width' and 'height' properties
(as well as other keyword values introduced by later specifications,
unless otherwise specified)
is not influenced by the 'box-sizing' property,
and always sets the size of the content box.
The following terms, whose definitions vary based on the computed value of 'box-sizing' are introduced:
<table border="1">
<tr>
<th>
<th>''box-sizing: content-box''
<th>''box-sizing: border-box''
<tr>
<td><dfn>min inner width</dfn>
<td>'min-width'
<td>max(0, 'min-width' − 'padding-left' − 'padding-right' − 'border-left-width' − 'border-right-width')
<tr>
<td><dfn>max inner width</dfn>
<td>'max-width'
<td>max(0, 'max-width' − 'padding-left' − 'padding-right' − 'border-left-width' − 'border-right-width')
<tr>
<td><dfn>min inner height</dfn>
<td>'min-height'
<td>max(0, 'min-height' − 'padding-top' − 'padding-bottom' − 'border-top-width' − 'border-bottom-width')
<tr>
<td><dfn>max inner height</dfn>
<td>'max-height'
<td>max(0, 'max-height' − 'padding-top' − 'padding-bottom' − 'border-top-width' − 'border-bottom-width')
</table>
The <a href="https://www.w3.org/TR/CSS21/visudet.html">Visual formatting model details</a> of [[!CSS21]] are written assuming ''box-sizing: content-box''. The following disambiguations are made to clarify the behavior for all values of 'box-sizing':
<ol>
<li>
In <a href="https://www.w3.org/TR/CSS21/visudet.html#blockwidth">10.3.3</a>,
the second <q>width</q> in the following phrase is to be interpreted as <a spec="css21">content width</a>:
<q>If 'width' is not ''width/auto'' and 'border-left-width' + 'padding-left' + 'width' + [...]</q>
<li>
In <a href="https://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-width">10.3.7</a>,
<q>width</q> is to be interpreted as <a spec="css21">content width</a> in the following equation:
<q>'left' + 'margin-left' + 'border-left-width' + 'padding-left' + 'width' + [...]</q>
<li>
In <a href="https://www.w3.org/TR/CSS21/visudet.html#min-max-widths">10.4</a>,
<q>width</q>, <q>height</q>, <q>min-width</q>, <q>max-width</q>, <q>min-height</q> and <q>max-height</q>
are respectively to be interpreted as
<a spec="css21">content width</a>, <a spec="css21">content height</a>, <a>min inner width</a>, <a>max inner width</a>, <a>min inner height</a> and <a>max inner height</a> in the following phrases:
<ol>
<li>
<q>The tentative used width is calculated [...]</q>
<li>
<q>If the tentative used width is greater than 'max-width',
the rules above are applied again,
but this time using the computed value of 'max-width' as the computed value for 'width'.</q>
<li>
<q>If the resulting width is smaller than 'min-width',
the rules above are applied again,
but this time using the value of 'min-width' as the computed value for 'width'.</q>
<li>
<q>Select from the table the resolved height and width values for the appropriate constraint violation.
Take the max-width and max-height as max(min, max) so that min ≤ max holds true.
In this table w and h stand for the results of the width and height computations [...]</q>
<li>
All instances of these words in the table
<li>
<q>Then apply the rules under "Calculating widths and margins" above, as if 'width' were computed as this value.</q>
</ol>
<li>
In <a href="https://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-height">10.6.4</a>,
<q>height</q> is to be interpreted as <a spec="css21">content height</a> in the following equation:
<q>'top' + 'margin-top' + 'border-top-width' + 'padding-top' + 'height' + [...]</q>
<li>
In <a href="https://www.w3.org/TR/CSS21/visudet.html#min-max-heights">10.7</a>,
<q>width</q>, <q>height</q>, <q>min-height</q> and <q>max-height</q>
are respectively to be interpreted as
<a spec="css21">content width</a>, <a spec="css21">content height</a>, <a>min inner height</a> and <a>max inner height</a> in the following phrases:
<ol>
<li>
<q>The tentative used height is calculated [...]</q>
<li>
<q>If this tentative height is greater than 'max-height',
the rules above are applied again, but this time using the value of 'max-height' as the computed value for 'height'.</q>
<li>
<q>If the resulting height is smaller than 'min-height',
the rules above are applied again,
but this time using the value of 'min-height' as the computed value for 'height'.</q>
<li>
<q>[...] use the algorithm under Minimum and maximum widths above to find the used width and height.
Then apply the rules under "Computing heights and margins" above,
using the resulting width and height as if they were the computed values.</q>
</ol>
</ol>
<div class="example">
<h4 id="box-sizing-example" class="no-num no-toc">Using box-sizing to evenly share space</h4>
This example uses box-sizing to evenly horizontally split
two divs with fixed size borders inside a div container,
which would otherwise require additional markup.
sample CSS:
<pre><code class="lang-css">
div.container {
width:38em;
border:1em solid black;
}
div.split {
box-sizing:border-box;
width:50%;
border:1em silver ridge;
float:left;
}
</code></pre>
sample HTML fragment:
<pre><code class="lang-markup">
<div class="container">
<div class="split">This div occupies the left half.</div>
<div class="split">This div occupies the right half.</div>
</div>
</code></pre>
demonstration of sample CSS and HTML:
<div style="width:38em; border:1em solid black"><div style="box-sizing:border-box; width:50%; border:1em silver ridge; float:left">This div should occupy the left half.</div><div style="box-sizing:border-box; width:50%; border:1em silver ridge; float:left">This div should occupy the right half.</div>The two divs above should appear side by side, each (including borders) 50% of the content width of their container. If instead they are stacked one on top of the other then your browser does not support 'box-sizing'.</div>
</div>
<h2 id="outline-props" caniuse="outline">Outline properties</h2>
At times, style sheet authors may want to create outlines around
visual objects such as buttons, active form fields, image maps, etc.,
to make them stand out. Outlines differ from borders in the following
ways:
<ol>
<li>Outlines do not take up space.
<li>Outlines may be non-rectangular.
<li>UAs often render outlines on elements in the :focus state.
</ol>
The outline properties control the style of these dynamic outlines.
The stacking of the rendering of these outlines is explicitly left up to implementations
to provide a better user experience per platform.
This supersedes the stacking of outlines as defined in <a href="https://www.w3.org/TR/CSS21/zindex.html">Appendix E of CSS 2.1</a> [[CSS21]].
<strong class="advisement">
Keyboard users,
in particular people with disabilities
who may not be able to interact with the page in any other fashion,
depend on the outline being visible
on elements in the :focus state,
thus authors must not make the outline invisible on such elements
without making sure an alternative highlighting mechanism is provided.
</strong>
The rendering of applying transforms to outlines is left explicitly undefined in CSS3-UI.
<h3 id="outline">Outlines Shorthand: the 'outline' property</h3>
<pre class="propdef">
Name: outline
Value: [ <'outline-color'> || <'outline-style'> || <'outline-width'> ]
Initial: see individual properties
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: see individual properties
Animation type: see individual properties
</pre>
<h3 id="outline-width">Outline Thickness: the 'outline-width' property</h3>
<pre class="propdef">
Name: outline-width
Value: <<line-width>>
Initial: medium
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: absolute length; ''0'' if the outline style is ''border-style/none''.
Animation type: <a href="https://drafts.csswg.org/css3-transitions/#animtype-length">length</a>
</pre>
<h3 id="outline-style">Outline Patterns: the 'outline-style' property</h3>
<pre class="propdef">
Name: outline-style
Value: auto | <<outline-line-style>>
Initial: none
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: as specified
</pre>
<h3 id="outline-color">Outline Colors: the 'outline-color' property</h3>
<pre class="propdef">
Name: outline-color
Value: <<color>> | invert
Initial: invert
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: The computed value for ''outline-color/invert'' is ''outline-color/invert''.
For <<color>> values, see <a>resolving color values</a> in [[!CSS-COLOR-4]].
Animation Type: <a href="https://drafts.csswg.org/css3-transitions/#animtype-color">color</a>
</pre>
The outline created with the outline properties is drawn "over" a box,
i.e., the outline is always on top,
and doesn't influence the position or size of the box,
or of any other boxes.
Therefore, displaying or suppressing outlines does not cause reflow.
Outlines may be non-rectangular.
For example, if the element is broken across several lines,
the outline should be an outline or minimum set of outlines
that encloses all the element's boxes.
Each part of the outline should be fully connected
rather than open on some sides
(as borders on inline elements are when lines are broken).
The parts of the outline are not required to be rectangular.
To the extent that the outline follows the <a>border edge</a>,
it should follow the 'border-radius' curve.
The position of the outline may be affected by descendant boxes.
User agents should use an algorithm for determining
the outline that encloses a region appropriate
for conveying the concept of focus to the user.
Note: This specification does not define the exact position or shape of the outline, but it is typically drawn immediately outside the border box.
The 'outline-width' property accepts
the same values as 'border-width'
([[css-backgrounds-3#the-border-width]]).
<dfn><<outline-line-style>></dfn> accepts
the same values as <<line-style>>
([[css-backgrounds-3#the-border-style]])
with the same meaning,
except that
<span class=css>hidden</span> is not a legal outline style.
In addition,
the 'outline-style' property
accepts the value ''outline-style/auto''.
The ''outline-style/auto'' value permits the user agent
to render a custom outline style,
typically a style which is either a user interface default for the platform,
or perhaps a style that is richer
than can be described in detail in CSS,
e.g. a rounded edge outline with semi-translucent outer pixels
that appears to glow.
As such, this specification does not define how the
'outline-color'
is incorporated or used (if at all) when rendering
''outline-style/auto'' style outlines.
User agents may treat ''outline-style/auto'' as
''outline-style/solid''.
The 'outline-color' property
accepts all colors, as well as the keyword <dfn dfn-type=value dfn-for=outline-color>invert</dfn>.
''outline-color/invert'' is expected to perform a color inversion on the pixels on the screen.
This is a common trick to ensure the focus border is visible,
regardless of color background.
Conformant UAs may ignore the ''outline-color/invert'' value
on platforms that do not support color inversion of the pixels on the screen.
If the UA does not support the ''outline-color/invert'' value
then it must reject that value at parse-time, and
the initial value of the 'outline-color' property
is the ''color/currentColor'' keyword.
The 'outline' property is a shorthand property,
and sets all three of 'outline-style',
'outline-width',
and 'outline-color'.
Note: The outline is the same on all sides.
In contrast to borders,
there are no ''outline-top'' or ''outline-left'' etc. properties.
This specification does not define how multiple overlapping outlines are drawn,
or how outlines are drawn for boxes that are partially obscured behind other elements.
<div class="example">
Here's an example of drawing a thick outline around a BUTTON element:
<pre><code class="lang-css">
button { outline: thick solid }
</code></pre>
</div>
Graphical user interfaces may use outlines around elements
to tell the user which element on the page has the focus.
These outlines are in addition to any borders,
and switching outlines on and off should not cause the document to reflow.
The focus is the subject of user interaction in a document
(e.g. for entering text or selecting a button).
<div class="example">
For example, to draw a thick black line around an element when it has the focus,
and a thick red line when it is active,
the following rules can be used:
<pre><code class="lang-css">
:focus { outline: thick solid black }
:active { outline: thick solid red }
</code></pre>
</div>
Note: Since the outline does not affect formatting
(i.e., no space is left for it in the box model),
it may well overlap other elements on the page.
<h3 id="outline-offset">Offsetting the Outline: the 'outline-offset' property</h3>
By default, the outline is drawn starting just outside the <a>border edge</a>.
However, it is possible to offset the outline and draw it beyond the <a>border edge</a>.
<pre class="propdef">
Name: outline-offset
Value: <<length>>
Initial: 0
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: <<length>> value in absolute units (px or physical).
Animation Type: <a href="https://drafts.csswg.org/css3-transitions/#animtype-length">length</a>
</pre>
If the computed value of 'outline-offset'
is anything other than 0,
then the outline is outset from the <a>border edge</a> by that amount.
<div class="example">
For example,
to leave 2 pixels of space between a focus outline
and the element that has the focus or is active,
the following rule can be used:
<pre><code class="lang-css">
:focus,:active { outline-offset: 2px }
</code></pre>
</div>
<p id=negative-offset>Negative values must cause the outline
to shrink into the border box.
Both the height and the width of outside of the shape
drawn by the outline should not become smaller
than twice the computed value of the 'outline-width' property,
to make sure that an outline can be rendered
even with large negative values.
User Agents should apply this constraint
independently in each dimension.
If the outline is drawn as multiple disconnected shapes,
this constraint applies to each shape separately.
<h2 id="resizing-and-overflow">Resizing & Overflow</h2>
CSS2.1 provides a mechanism for controlling the appearance of a scrolling mechanism
(e.g. scrollbars)
on block container elements.
This specification adds to that a mechanism for controlling
user resizability of elements as well as the ability to specify text overflow behavior.
<h3 id="resize" caniuse="css-resize">Resizing Boxes: the 'resize' property</h3>
The 'resize' property allows the author
to specify whether or not an element is resizable by the user,
and if so, along which axis/axes.
<pre class="propdef">
Name: resize
Value: none | both | horizontal | vertical
Initial: none
Applies to: elements with 'overflow' other than visible,
and optionally replaced elements such as images, videos, and iframes
Inherited: no
Percentages: N/A
Media: visual
Computed value: as specified
</pre>
<dl>
<dt>none
<dd>The UA does not present a resizing mechanism on the element,
and the user is given no direct manipulation mechanism to resize the element.
<dt>both
<dd>The UA presents a bidirectional resizing mechanism
to allow the user to adjust both the height and the width of the element.
<dt>horizontal
<dd>The UA presents a unidirectional horizontal resizing mechanism
to allow the user to adjust only the width of the element.
<dt>vertical
<dd>The UA presents a unidirectional vertical resizing mechanism
to allow the user to adjust only the height of the element.
</dl>
Currently it is possible to control the appearance of the scrolling mechanism (if any)
on an element using the 'overflow' property
(e.g. <code class="lang-css">overflow: scroll</code> vs. <code class="lang-css">overflow: hidden</code> etc.).
The purpose of the 'resize' property
is to allow control over the appearance and function of the resizing mechanism
(e.g. a resize box or widget) on the element.
Note: The resizing mechanism is NOT the same as the scrolling mechanism,
nor is it related to any UA mechanism for zooming.
The scrolling mechanism allows the user
to determine which portion of the contents of an element is shown.
The resizing mechanism allows the user
to determine the size of the element.
The 'resize' property applies to elements
whose computed 'overflow' value
is something other than ''visible''.
UAs may also apply it,
regardless of the value of the 'overflow' property,
to:
<ul>
<li>Replaced elements representing images or videos, such as <{img}>, <{video}>, <{picture}>, <{svg}>, <{object}>, or <{canvas}>.
<li>The <{iframe}> element.
</ul>
The effect of the 'resize' property on generated content is undefined.
Implementations should not apply the 'resize' property to generated content.
Note: the 'resize' property may apply to generated content in the future
if there is implementation of <a href="https://drafts.csswg.org/css-pseudo/#CSSPseudoElement-interface">Interface CSSPseudoElement</a>.
When an element is resized by the user,
the user agent sets
the 'width' and 'height' properties
to px unit length values of the size indicated by the user,
in the element’s <a href="https://www.w3.org/TR/css-style-attr/#style-attribute">style attribute</a> DOM,
replacing existing property declaration(s), if any,
without ''!important'', if any.
If an element is resized in only one dimension,
only the corresponding property is set, not both.
The precise direction of resizing
(i.e. altering the top left of the element or altering the bottom right)
may depend on a number of CSS layout factors
including whether the element is absolutely positioned,
whether it is positioned using the 'right'
and 'bottom' properties,
whether the language of the element is right-to-left etc.
The UA should consider the direction of resizing
(as determined by CSS layout),
as well as platform conventions and constraints when deciding
how to convey the resizing mechanism to the user.
The user agent must allow the user to resize the element
with no other constraints than what is imposed by
'min-width', 'max-width', 'min-height', and 'max-height'.
Note: There may be situations where user attempts to resize an element
appear to be overriden or ignored, e.g. because of ''!important'' cascading declarations that supersede
that element’s <a href="https://www.w3.org/TR/css-style-attr/#style-attribute">style attribute</a>
'width' and 'height' properties in the DOM.
Changes to the computed value of an element's 'resize' property
do not reset changes to the <a href="https://www.w3.org/TR/css-style-attr/#style-attribute">style attribute</a> made due to
user resizing of that element.
<div class="example">
For example,
to make iframes scrollable <em>and</em> resizable,
the following rule can be used:
<pre><code class="lang-css">
iframe,object[type^="text/"],
object[type$="+xml"],object[type="application/xml"]
{
overflow:auto;
resize:both;
}
</code></pre>
</div>
<h3 id="text-overflow" caniuse="text-overflow">Overflow Ellipsis: the 'text-overflow' property</h3>
<pre class="propdef">
Name: text-overflow
Value: [ clip | ellipsis | <<string>> | fade | <<fade()>> ]{1,2}
Initial: clip
Applies to: block containers
Inherited: no
Percentages: refer to the width of the line box
Media: visual
Computed value: As specified, with <<length>> converted to absolute units
</pre>
This property specifies rendering when inline content overflows
its line box edge
in the inline progression direction of its block container element ("the block")
that has 'overflow'
other than ''visible''.
Text can overflow for example when it is prevented from wrapping
(e.g. due to <code class="lang-css">white-space: nowrap</code>
or a single word is too long to fit).
Values have the following meanings:
<dl dfn-for="text-overflow" dfn-type=value>
<dt><dfn id=overflow-clip>clip</dfn>
<dd>
Clip inline content that overflows its block container element.
Characters may be only partially rendered.
<dt><dfn id=overflow-ellipsis>ellipsis</dfn>
<dd>
Render an ellipsis character (U+2026)
to represent clipped inline content.
Implementations may substitute a more language, script, or writing-mode appropriate
ellipsis character,
or three dots "..." if the ellipsis character is unavailable.
<dt id=overflow-string><<string>>
<dd>
Render the given string to represent clipped inline content.
The given string is treated as an independent paragraph
for bidi purposes.
<dt dfn-type=function><dfn>fade( <<length>> | <<percentage>> )</dfn>
<dd>
Clip inline content that overflows its line box.
Characters may be only partially rendered.
In addition, the UA must apply a fade out effect
near the edge of the line box,
reaching complete transparency at the edge.
Issue: Do we need to define the way
the fade out is calculated
so that the fading is identical across browsers?
It should probably be something like
''mask-image: linear-gradient(to right, rgba(0,0,0,1), rgba(0,0,0,0))'',
except applied to the relevant portion of the line only.
The argument determines the distance
over which the fade effect is applied.
The <<percentage>> is resolved against the width of the line box.
Values lower than 0 are clipped to 0.
Values greater than the width of the line box are clipped to the width of the line box.
Issue: If the line box is too short
to display the fade effect at the desired length,
should we drop the effect,
or shrink the distance it is applied over until it fits,
or clip the end of the fade?
Issue: How should we deal with
things overflowing out of the line box,
or overlapping onto it?
Should fade apply to the logical content of the line,
or to the physical area of the line box,
or the intersection of both?
<dt><dfn>fade</dfn>
<dd>
Same as ''fade()'',
but the distance over which the fading effect is applied
is determined by the UA.
''1em'' is suggested as a reasonable value.
</dl>
The term "character" is used in this property definition
for better readability and means "grapheme cluster" [[!UAX29]]
for implementation purposes.
If there is one value,
it applies only to the <a>end</a> line box edge.
If there are two values,
the first value applies to the <a>line-left</a> edge,
and the second value applies to the <a>line-right</a> edge.
The terms <a>end</a>, <a>line-left</a> and <a>line-right</a> are defined in [[!CSS-WRITING-MODES-3]].
Note: the use of <a>line-left</a> and <a>line-right</a>
rather than <a>start</a> and <a>end</a>
when there are two values is intentional,
to facilitate the use of directional characters such as arrows.
For the ellipsis
and string values,
implementations must hide characters and
<a href="https://www.w3.org/TR/CSS21/visuren.html#inline-boxes">
atomic inline-level elements</a>
at the applicable edge(s) of the line as necessary to fit the ellipsis/string, and
place the ellipsis/string immediately adjacent
to the applicable edge(s) of the remaining inline content.
The first character or
<a href="https://www.w3.org/TR/CSS21/visuren.html#inline-boxes">
atomic inline-level element</a>
on a line
must be clipped rather than ellipsed.
<div class=example>
<h4 id="bidi-ellipsis" class="no-num no-toc">Bidi ellipsis examples</h4>
These examples demonstrate which characters get hidden
to make room for the ellipsis in a bidi situation:
those visually at the edge of the line.
Sample CSS:
<pre><code highlight=css>
div {
font-family: monospace;
white-space: pre;
overflow: hidden;
width: 9ch;
text-overflow: ellipsis;
}
</code></pre>
Sample HTML fragments, renderings, and your browser:
<table class="awesome-table data">
<thead><th>HTML<th>Reference rendering<th>Your Browser</thead>
<tr>
<td><code highlight=html><div>שלום 123456</div></code><td><div style="font-family:monospace">123456 ם…</div><td><div style="font-family: monospace; white-space: pre; overflow: hidden; width: 9ch; text-overflow: ellipsis">שלום 123456</div>
<tr><td><code highlight=html><div dir=rtl>שלום 123456</div></code><td><div style="font-family:monospace">…456 שלום</div><td><div style="font-family: monospace; white-space: pre; overflow: hidden; width: 9ch; text-overflow: ellipsis" dir=rtl>שלום 123456</div>
</table>
</div>
<h4 id="ellipsing-details" class="no-num no-toc">ellipsing details</h4>
<ul>
<li>
Ellipsing only affects rendering and must not affect layout
nor dispatching of pointer events:
The UA should dispatch any pointer event on the ellipsis to the elided element,
as if 'text-overflow' had been ''text-overflow/none''.
<li>
The ellipsis is styled and baseline-aligned according to the block.
<li>
Ellipsing occurs after relative positioning and other graphical transformations.
<li>
If there is insufficient space for the ellipsis,
then clip the rendering of the ellipsis itself
(on the same side that neutral characters on the line
would have otherwise been clipped with the ''text-overflow:clip'' value).
</ul>
<h4 id="ellipsis-interaction" class="no-num no-toc">user interaction with ellipsis</h4>
<ul>
<li>
When the user is interacting with content
(e.g. editing, selecting, scrolling),
the user agent may treat ''text-overflow/ellipsis'', string values, ''overflow-text/fade'' or ''overflow-text/fade()'' as ''text-overflow:clip''.
<li>
Selecting the ellipsis should select the ellipsed text.
If all of the ellipsed text is selected,
UAs should show selection of the ellipsis.
Behavior of partially-selected ellipsed text is up to the UA.
</ul>
<div class="example">
<h4 id="text-overflow-examples" class="no-num no-toc">text-overflow examples</h4>
These examples demonstrate setting the text-overflow of a block container element
that has text which overflows its dimensions:
sample CSS for a div:
<pre><code class="lang-css">
div {
font-family: Helvetica, sans-serif;
line-height: 1.1;
width: 3.1em;
border: solid .1em black;
padding: 0.2em; margin:1em 0;
}
</code></pre>
sample HTML fragments, renderings, and your browser:
<table class="awesome-table"><tbody>
<tr>
<th>HTML
<th>sample rendering
<th>your browser
<tr>
<td>
<pre><code class="lang-markup">
<div>
CSS IS AWESOME, YES
</div>
</code></pre>
<td>
<object type="image/png" data="images/cssisawesome.png">
First, a box with text drawing outside of it.
</object>
<td>
<div style="width:3.1em; border:solid .1em black; margin:1em 0; padding:.2em; font-family:Helvetica,sans-serif; line-height:1.1;">CSS IS AWESOME, YES</div>
<tr>
<td>
<pre><code class="lang-markup">
<div style="<strong>text-overflow:clip;</strong> overflow:hidden">
CSS IS AWESOME, YES
</div>
</code></pre>
<td>
<object type="image/png" data="images/cssisaweso.png">
Second, a similar box with the text clipped outside the box.
</object>
<td>
<div style="width:3.1em; border:solid .1em black; margin:1em 0; padding:.2em; font-family:Helvetica,sans-serif; line-height:1.1; overflow:hidden;text-overflow:clip;">CSS IS AWESOME, YES</div>
<tr>
<td>
<pre><code class="lang-markup">
<div style="<strong>text-overflow:ellipsis;</strong> overflow:hidden">
CSS IS AWESOME, YES
</div>
</code></pre>
<td>
<object type="image/png" data="images/cssisaw.png">
Third, a similar box with an ellipsis representing the clipped text.
</object>
<td>
<div style="width:3.1em; border:solid .1em black; margin:1em 0; padding:.2em; font-family:Helvetica,sans-serif; line-height:1.1; overflow:hidden;text-overflow:ellipsis;">CSS IS AWESOME, YES</div>
<tr>
<td>
<pre><code class="lang-markup">
<div style="<strong>text-overflow:ellipsis;</strong> overflow:hidden">
NESTED
<p>PARAGRAPH</p>
WON'T ELLIPSE.
</div>
</code></pre>
<td>
<object type="image/png" data="images/nes.png">
Fourth, a box with a nested paragraph demonstrating anonymous block boxes equivalency and non-inheritance into a nested element.
</object>
<td>
<div style="width:3.1em; border:solid .1em black; margin:1em 0; padding:.2em; font-family:Helvetica,sans-serif; line-height:1.1; overflow:hidden;text-overflow:ellipsis;">NESTED
<p>PARAGRAPH</p>
WON'T ELLIPSE.</div>
<tr>
<td>
<pre><code class="lang-markup">
<div style="<strong>text-overflow:fade;</strong> overflow:hidden">
CSS IS AWESOME, YES
</div>
</code></pre>
<td>
<object type="image/png" data="images/cssisfade.png">
a box with the text fading out on overflow.
</object>
<td>