Contents
The position and size of an element's box(es) are sometimes
computedcalculated relative to a certain rectangle, called the containing
block of the element. The containing block of an element
is defined as follows:
Note: This may cause the containing block's width to be negative.
If there is no such ancestor, the content edge of the root element's box establishes thecontaining block. Example(s): With no positioning,block is the initial
containing blocks (C.B.)block.
In the following document: <HTML> <HEAD> <TITLE>Illustration of containing blocks</TITLE> </HEAD> <BODY id="body"> <DIV id="div1"> <P id="p1">Thispaged media, an absolutely positioned element is text inpositioned
relative to its containing block ignoring any page breaks (as if the
first paragraph...</P> <P id="p2">This is text <EM id="em1"> indocument were continuous). The <STRONG id="strong1">second</STRONG> paragraph.</EM></P> </DIV> </BODY> </HTML>element may subsequently be broken over
several pages.
For absolutely positioned content that resolves to a position on a page other than the page being laid out (the current page), or resolves to a position on the current page which has already been rendered for printing, printers may place the content
Note that a block-level element that is split over several pages may have a different width on each page and that there may be device-specific limits.
With no positioning, the containing blocks (C.B.) in the following document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<HTML>
<HEAD>
<TITLE>Illustration of containing blocks</TITLE>
</HEAD>
<BODY id="body">
<DIV id="div1">
<P id="p1">This is text in the first paragraph...</P>
<P id="p2">This is text <EM id="em1"> in the
<STRONG id="strong1">second</STRONG> paragraph.</EM></P>
</DIV>
</BODY>
</HTML>
are established as follows:
| For box generated by | C.B. is established by |
|---|---|
| | initial C.B. (UA-dependent) |
| body | html |
| div1 | body |
| p1 | div1 |
| p2 | div1 |
| em1 | p2 |
| strong1 | p2 |
If we position "div1":
#div1 { position: absolute; left: 50px; top: 50px }
its containing block is no longer "body"; it becomes the initial containing block (since there are no other positioned ancestor boxes).
If we position "em1" as well:
#div1 { position: absolute; left: 50px; top: 50px }
#em1 { position: absolute; left: 100px; top: 100px }
the table of containing blocks becomes:
| For box generated by | C.B. is established by |
|---|---|
| | initial C.B. (UA-dependent) |
| body | html |
| div1 | initial C.B. |
| p1 | div1 |
| p2 | div1 |
| em1 | div1 |
| strong1 | em1 |
By positioning "em1", its containing block becomes the nearest positioned ancestor box (i.e., that generated by "div1").
| Value: | <length> | <percentage> | auto | inherit |
| Initial: | auto |
| Applies to: | all elements but non-replaced inline elements, table rows, and row groups |
| Inherited: | no |
| Percentages: | refer to width of containing block |
| Media: | visual |
| Computed value: | the percentage or 'auto' as specified or the absolute length; 'auto' if the property does not apply |
This property specifies the content width of boxes generated by block-level and replaced elements.
This property does not apply to non-replaced inline-level elements. The content width of a non-replaced inline element's boxes is that of the rendered content within them (before any relative offset of children). Recall that inline boxes flow into line boxes. The width of line boxes is given by the their containing block, but may be shorted by the presence of floats.
The width of a replaced element's box is intrinsic and may be scaled by the user agent if the value of this property is different than 'auto'.
Values have the following meanings:
Negative values for 'width' are illegal.
For example, the following rule fixes the content width of paragraphs at 100 pixels:
p { width: 100px }
The computedvalues of an element's 'width', 'margin-left', 'margin-right', 'left' and 'right' properties as used for layout
depend on the type of box generated and on each other. (The value used
for layout is sometimes referred to as the used value.) In
principle, the computedvalues used are the same as the specifiedcomputed values, with
'auto' replaced by some suitable value, and percentages calculated
based on the containing block, but there are exceptions. The following
situations need to be distinguished:
For Points 1-6 include relative positioning.and 9-10, the values of 'left' and 'right' used for
layout are determined by the rules in section 9.4.3.
The 'width' property does not
apply. A specifiedcomputed value of 'auto' for 'left', 'right', 'margin-left' or 'margin-right' becomes a computedused
value of '0'.
A specifiedcomputed value of 'auto' for 'left' , 'right' ,'margin-left' or 'margin-right' becomes a computedused
value of '0'.
If 'width' has a specifiedcomputed value
of 'auto' for 'width' givesand 'height' also has a
computed value of 'auto', the element's intrinsic width asis the used value of
'width', if it has one.
If 'width' has a computed value
of 'auto' and 'height' has some
other computed value, and the replaced element has an intrinsic ratio,
or, if both 'width' and 'height' have computed value.values of
'auto', and the element has no intrinsic width but does have an
intrinsic height and intrinsic ratio, then the used value of 'width' is:
(intrinsic ratio) * (used height)
Otherwise, if 'width' has a computed value of 'auto', but none of the conditions above are met, then the used value of 'width' becomes 300px. If 300px is too wide to fit the device, UAs should use the width of the largest rectangle that has a 2:1 ratio and fits the device instead.
Percentage intrinsic widths are first evaluated with respect to the containing block's width, if that width doesn't itself depend on the replaced element's width. If it does, then a percentage intrinsic width on that element can't be resolved and the element is assumed to have no intrinsic width.
If 'left' or 'right' are given as 'auto', their computed value is 0.The following constraints must hold
betweenamong the used values of the other properties:
'margin-left' + 'border-left-width' + 'padding-left' + 'width' + 'padding-right' + 'border-right-width' + 'margin-right' = width of containing block
(If the border styleIf 'width' is 'none', use '0' asnot 'auto' and 'border-left-width' + 'padding-left' +
'width' + 'padding-right' + 'border-right-width' (plus any of
'margin-left' or 'margin-right' that are not 'auto') is larger than
the border width.)width of the containing block, then any 'auto' values for
'margin-left' or 'margin-right' are, for the following rules, treated
as zero.
If
all of the above have a specifiedcomputed value other than 'auto', the values
are said to be "over-constrained" and one of the computedused values will
have to be different from its specifiedcomputed value. If the 'direction'
property of the containing block has the value 'ltr', the specified
value of 'margin-right' is ignored and the
value is computedcalculated so as to make the equality true. If the value of
'direction' is 'ltr','rtl', this
happens to 'margin-left' instead.
If there is exactly one value specified as 'auto', its computedused
value follows from the equality.
If 'width' is set to 'auto', any other 'auto' values become '0' and 'width' follows from the resulting equality.
If both 'margin-left' and
'margin-right' are 'auto',
their computedused values are equal. This horizontally centers the element
with respect to the edges of the containing block.
If 'left' or 'right' are 'auto', their computedThe used value is 0. Ifof
'width' is specifieddetermined
as 'auto', its value is the element's intrinsic width. If one of the margins is 'auto', its computed value is given byfor inline replaced
elements.
Then the constraints above. Furthermore, if both margins are 'auto', their computed valuesrules for non-replaced
block-level elements are equal.applied to determine the margins.
If 'left' , 'right' , 'width' ,'margin-left', or 'margin-right' are specifiedcomputed as
'auto', their computedused value is '0'.
If 'width' is computed as 'auto', the used value is the "shrink-to-fit" width.
Calculation of the shrink-to-fit width is similar to calculating the width of a table cell using the automatic table layout algorithm. Roughly: calculate the preferred width by formatting the content without breaking lines other than where explicit line breaks occur, and also calculate the preferred minimum width, e.g., by trying all possible line breaks. CSS 2.1 does not define the exact algorithm. Thirdly, find the available width: in this case, this is the width of the containing block minus the used values of 'margin-left', 'border-left-width', 'padding-left', 'padding-right', 'border-right-width', 'margin-right', and the widths of any relevant scroll bars.
Then the shrink-to-fit width is: min(max(preferred minimum width, available width), preferred width).
If 'left' , 'right' ,'margin-left' or 'margin-right' are specifiedcomputed as
'auto', their computedused value is '0'. If 'width' is 'auto', itsThe used value of 'width' is the element's intrinsic width.determined as for inline replaced elements.
The constraint that determines the computed valuesFor these elements is: 'left' + 'margin-left' + 'border-left-width' + 'padding-left' + 'width' + 'padding-right' + 'border-right-width' + 'margin-right' + 'right' = width of containing block (Ifthe border style is 'none', use '0' aspurposes of this section and the border width.)next, the solutionterm "static position"
(of an element) refers, roughly,
to this constraint is reached through a number of substitutionsthe position an element would have had in the following order: If 'left' hasnormal flow. More
precisely:
If 'width'But rather than actually calculating the dimensions of that
hypothetical box, user agents are free to make a guess at its probable
position.
For the purposes of calculating the static position, the containing
block of fixed positioned elements is 'auto', replace any remaining 'auto'the initial containing block
instead of the viewport, and all scrollable boxes should be assumed to
be scrolled to their origin.
The constraint that determines the used values for these elements is:
'left'
or+ 'margin-left' + 'border-left-width' + 'padding-left' + 'width' + 'padding-right' + 'border-right-width' + 'margin-right' + 'right'with'0'.= width of containing block
If 'left' ,all three of 'left', 'width', and 'right' or 'width'are (still) 'auto', replace'auto': First set
any 'auto' onvalues for 'margin-left' orand 'margin-right' with '0'.to 0. Then, if
the 'direction' property of the containing block is 'ltr' set 'left'
to the static position and apply rule number
three below; otherwise, set 'right' to the static position and apply rule number
one below.
If none of the three is 'auto': If at this pointboth 'margin-left' and
'margin-right' are still'auto', solve the
equation under the extra constraint that the two margins mustget equal
values. If atvalues, unless this point therewould make them negative, in which case when
direction of the containing block is only'ltr' ('rtl'), set 'margin-left'
('margin-right') to zero
and solve for 'margin-right' ('margin-left'). If one 'auto' left,of
'margin-left' or 'margin-right' is 'auto', solve the equation for that
value. If at this pointthe values are over-constrained, ignore the value for either'left'
(in case the 'direction' property of the containing block is 'rtl') or
'right' (in case 'direction' is
'ltr') and solve for that value.
10.3.8 Absolutely positioned, replaced elements This situation is similarOtherwise, set 'auto' values for 'margin-left' and 'margin-right'
to 0, and pick the previous one, except that the element has an intrinsic width. The sequenceone of substitutions is now: Ifthe following six rules that applies.
Calculation of the shrink-to-fit width is similar to calculating the width of a table cell using the automatic table layout algorithm. Roughly: calculate the preferred width by formatting the content without breaking lines other than where explicit line breaks occur, and also calculate the preferred minimum width, e.g., by trying all possible line breaks. CSS 2.1 does not define the exact algorithm. Thirdly, calculate the available width: this is found by solving for 'width' after setting 'left' (in case 1) or 'right' (in case 3) to 0.
Then the shrink-to-fit width is: min(max(preferred minimum width, available width), preferred width).
This situation is similar to the previous one, except that the element has an intrinsic width. The sequence of substitutions is now:
If 'width' is 'auto', the used value is the shrink-to-fit width as for floating elements.
A computed value of 'auto' for 'margin-left' or 'margin-right' becomes a used value of '0'.
Exactly as inline replaced elements.
| Value: | <length> | <percentage> | inherit |
| Initial: | 0 |
| Applies to: | all elements but non-replaced inline elements, table rows, and row groups |
| Inherited: | no |
| Percentages: | refer to width of containing block |
| Media: | visual |
| Computed value: | the percentage as specified or the absolute length |
| Value: | <length> | <percentage> | none | inherit |
| Initial: | none |
| Applies to: | all elements but non-replaced inline elements, table rows, and row groups |
| Inherited: | no |
| Percentages: | refer to width of containing block |
| Media: | visual |
| Computed value: | the percentage as specified or the absolute length or 'none' |
These two properties allow authors to constrain content widths to a certain range. Values have the following meanings:
Negative values for 'min-width' and 'max-width' are illegal.
The following algorithm describes how the two properties influence the used value of the 'width' property:
However, for replaced elements with an intrinsic ratio and both 'width' and 'height' specified as 'auto', the algorithm is as follows:
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 ignoring the 'min-width', 'min-height', 'max-width' and 'max-height' properties. Normally these are the intrinsic width and height, but they may not be in the case of replaced elements with intrinsic ratios.
| Constraint Violation | Resolved Width | Resolved Height |
|---|---|---|
| none | w | h |
| w > max-width | max-width | max(max-width * h/w, min-height) |
| w < min-width | min-width | min(min-width * h/w, max-height) |
| h > max-height | max(max-height * w/h, min-width) | max-height |
| h < min-height | min(min-height * w/h, max-width) | min-height |
| (w > max-width) and |
max-width | max(min-height, max-width * h/w) |
| (w > max-width) and |
max(min-width, max-height * w/h) | max-height |
| (w < min-width) and (h < min-height), where (min-width/w ≤ min-height/h) | min(max-width, min-height * w/h) | min-height |
| (w < min-width) and (h < min-height), where (min-width/w > min-height/h) | min-width | min(max-height, min-width * h/w) |
| (w < min-width) and (h > max-height) | min-width | max-height |
| (w > max-width) and (h < min-height) | max-width | min-height |
Then apply the rules under "Calculating widths : 'min-width'and
'max-width' 'min-width'margins" above, as if 'width'
were computed as this value.
| Value: | <length> | <percentage> | auto | inherit |
| Initial: | |
| Applies to: | all elements |
| Inherited: | no |
| Percentages: | |
| Media: | visual |
| | |
This property specifies the content height of boxes generated by block-level, inline-block and replaced elements.
This property does not apply to non-replaced inline elementsinline-level elements. See the section on computing heights and tablemargins
for non-replaced inline elements Inherited: no Percentages: refer to width of containing block Media: visual These two properties allow authors to constrain box widths to a certain range.for the rules used instead.
Values have the following meanings:
Note that the following algorithm describes howheight of the two properties influencecontaining block of an
absolutely positioned element is independent of the computed valuesize of the
'width' property:element itself, and thus a percentage height on such an element can
always be resolved. However, it may be that the widthheight is computed (without 'min-width' and 'max-width' ) followingnot known
until elements that come later in the rules under "Computing widths and margins" above. Ifdocument have been processed.
Negative values for 'height' are illegal.
For example, the computed value of 'min-width' is greater thanfollowing rule sets the valuecontent height of 'max-width' , 'max-width' is setparagraphs
to 100 pixels:
p { height: 100px }
Paragraphs of which the valueheight of 'min-width' . Ifthe computed width is greater than 'max-width' ,contents exceeds 100 pixels
will overflow according to the
rules above are applied again, but this time using'overflow' property.
For calculating the valuevalues of 'max-width' as the specified value'top', 'margin-top', 'height',
'margin-bottom', and 'bottom' a distinction must be made between
various kinds of boxes:
For 'width' . IfPoints 1-6 and 9-10, the computed width is smaller than 'min-width' ,used values of 'top' and
'bottom' are determined by the rules above are applied again, but this time usingin section 9.4.3.
Note: these rules apply to
the value of 'min-width'root element just as to any other element.
The specified value for 'width' .'height' property doesn't
apply. The user agent may define a non-negative minimum value forheight of the 'min-width' property, which may vary from element to element and even dependcontent area should be based on other properties. If 'min-width' goes belowthe font, but
this limit, either because it was set explicitly,specification does not specify how. A UA may, e.g., use the
em-box or because it was 'auto'the maximum ascender and descender of the rules belowfont. (The latter
would make it too small, the user agent may useensure that glyphs with parts above or below the minimum value asem-box still
fall within the computed value. 10.5content height : the 'height' property 'height' Value: <length> | <percentage> | auto | inherit Initial: auto Applies to: all elementsarea, but non-replaced inline elements, table columns, and column groups Inherited: no Percentages: see prose Media: visual This property specifiesleads to differently sized boxes for
different fonts; the former would ensure authors can control
background styling relative to the 'line-height', but leads to glyphs
painting outside their content heightarea.)
Note: level 3 of boxes generated by block-level and replaced elements. ThisCSS will probably include a property does not applyto
non-replaced inline-level elements. The heightselect which measure of a non-replaced inline element's boxes is given bythe element's (possibly inherited) 'line-height' value. Values havefont is used for the following meanings: <length> Specifies a fixed height. <percentage> Specifies a percentagecontent height.
The percentagevertical padding, border and margin of an inline, non-replaced
box start at the top and bottom of the content area, not the 'line-height'. But only the 'line-height' is calculated with respect toused when calculating
the height of the generated box's containing block .line box.
If more than one font is
used (this could happen when glyphs are found in different fonts), the
height of the containing block is not specified explicitly (i.e., it depends oncontent height), the valuearea is interpreted like 'auto'. autonot defined by this specification.
However, we suggest that the height depends on the values of other properties. Seeis chosen such that the prose below. Negative values for 'height' are illegal. Example(s):content
area is just high enough for example,either (1) the following rule fixesem-boxes, or (2) the
heightmaximum ascenders and descenders, of paragraphs to 100 pixels: P { height: 100px } Paragraphsall the fonts in the
element. Note that require morethis may be larger than 100 pixelsany of height will overflow according tothe 'overflow' property. 10.6 Computing heights and margins For computingfont sizes
involved, depending on the values of 'top' , 'margin-top' , 'height' , 'margin-bottom' , and 'bottom' a distinction must be made between various kindsbaseline alignment of boxes: inline, non-replaced elements inline,the fonts.
Points 1-6 include relative positioning. 10.6.1 Inline, non-replaced elementsIf 'top' , 'bottom' , 'margin-top' , or 'margin-bottom' are'margin-top', or 'margin-bottom' are 'auto',
their used value is 0.
If 'height' has a computed value of 'auto' and 'width' also has a computed value of 'auto', the element's intrinsic height is the used value of 'height', it has one.
If 'height' has a computed
value of 'auto' and 'width' has
some other computed value, and the replaced element has an intrinsic
ratio, or, if both 'height' and
'width' have computed values of
'auto', theirand the element has no intrinsic height but does have an
intrinsic width and intrinsic ratio, then the used value of 'height' is:
(used width) / (intrinsic ratio)
Otherwise, if 'height' has a
computed value is 0.of 'auto', but none of the conditions above are met,
then the used value of 'height'
property doesn't apply, butmust be set to 150px. If 300px is too wide to fit the device width,
UAs should use the height of the boxlargest rectangle that has a 2:1
ratio and fits the device width instead.
Percentage intrinsic heights are evaluated with respect to the
containing block's height, if that height is given byspecified explicitly, or
if the 'line-height' property. 10.6.2 Inline,replaced elements block-level,element is absolutely positioned. If neither of these
conditions is met, then percentage values on such replaced elements
in normal flow,can't be resolved and floating, replacedsuch elements If 'top' , 'bottom' , 'margin-top' , or 'margin-bottom'are 'auto', their computed value is 0. If 'height' is 'auto',assumed to have no intrinsic
height.
For 'inline' and 'inline-block' elements, the computed valuemargin box is used
when calculating the intrinsic height.height of the line box.
If 'top' , 'bottom' ,'margin-top', or 'margin-bottom' are 'auto',
their computedused value is 0. If 'height' is 'auto', the height depends
on whether the element has any block-level children.children and whether it has
padding or borders:
If it only has inline-level children, the heightheight is the distance
between the top of the topmost line box and the bottom of the
bottommost line box.
If
it has block-level children, the height is the distance between the
top border-edge of the topmost block-level child box that doesn't have
margins collapsed through it
and the bottom border-edge of the bottommost block-level child box
that doesn't have margins collapsed through it. However, if the
element has a non-zero top padding and/or top border, or is fromthe root
element, then the content
starts at the top margin edge of the topmost line box tochild. (The
first case expresses the fact that the top and bottom margins of the
element collapse with those
of the topmost and bottommost line box. If it has block-levelchildren, it iswhile in the distance fromsecond case the
top border-edgepresence of the topmost block-level child box, topadding/border prevents the top margins from collapsing.) Similarly, if the
element has a non-zero bottom border-edgepadding and/or bottom border, then the
content ends at the bottom margin edge of the bottommost
block-level child box.child.
Only children in the normal flow are taken into account (i.e., floating boxes and absolutely positioned boxes are ignored, and relatively positioned boxes are considered without their offset). Note that the child box may be an anonymous block box.
For absolutely positioned elements,the vertical dimensions must satisfy this constraint: 'top' + 'margin-top' + 'border-top-width' + 'padding-top' + 'height' + 'padding-bottom' + 'border-bottom-width' + 'margin-bottom' + 'bottom' = heightpurposes of containing block (If the border style is 'none', use '0' asthis section and the border width.)next, the solutionterm "static
position" (of an element) refers, roughly, to this constraint is reached through a number of substitutionsthe position an element
would have had in the following order: If 'top' hasnormal flow. More precisely, the value 'auto' replace it withstatic position
for 'top' is the distance from the top edge of the containing block to
the top margin edge of a hypothetical box that would have been the
first box of the element if its 'position' property had been
'static'. (But'static' and 'float' had been
'none'.
The value is negative if the hypothetical box is above the containing
block.
But rather than actually computingcalculating the dimensions of that
hypothetical box, user agents are free to make a guess at its probable
position.)position.
For the value is negative ifpurposes of calculating the hypothetical boxstatic position, the containing
block of fixed positioned elements is abovethe initial containing block. If bothblock
instead of the viewport.
For absolutely positioned elements, the used values of the vertical dimensions must satisfy this constraint:
'top' + 'margin-top' + 'border-top-width' + 'padding-top' + 'height' + 'padding-bottom' + 'border-bottom-width' + 'margin-bottom' + 'bottom' = height of containing block
If all three of 'top', 'height', and 'bottom' are 'auto', replace 'bottom' with 0.auto, set 'top'
to the static position and apply rule number three below.
If 'bottom' or 'height'none of the three are (still) 'auto', replace any 'auto' on 'margin-top' or 'margin-bottom' with '0'.'auto': If at this pointboth 'margin-top' and
'margin-bottom' are still'auto', solve the equation under the extra
constraint that the two margins mustget equal values. If at this point there is onlyone 'auto' left,of
'margin-top' or 'margin-bottom' is 'auto', solve the equation for that
value. If at this pointthe values are over-constrained, ignore the value for
'bottom' and solve for that value.
10.6.5 Absolutely positioned, replaced elements This situation is similar toOtherwise, pick the previous one, except thatone of the element has an intrinsic height.following six rules that
applies.
This situation is similar to make a guess at its probable position.)the previous one, except that the
element has an intrinsic height. The
sequence of substitutions is now:
If 'margin-top', or 'margin-bottom' are 'auto', their used value is 0. If 'height' is 'auto', the height depends on the element's descendants.
For 'inline-block' elements, the margin box is used when calculating the height of the line box.
In certain cases (see the preceding sections), the height of an element is computed as follows:
If it only has inline-level children, the height is the distance between the top of the topmost line box and the bottom of the bottommost line box.
If it has block-level children, the height is the distance between the top margin-edge of the topmost block-level child box and the bottom margin-edge of the bottommost block-level child box.
Absolutely positioned children are ignored, and relatively positioned boxes are considered without their offset. Note that the child box may be an anonymous block box.
In addition, if the element has any floating descendants whose bottom margin edge is below the bottom, then the height is increased to include those edges. Only floats that are children of the element itself or of descendants in the normal flow are taken into account, e.g., floats inside absolutely positioned descendants or other floats are not.
It is sometimes useful to constrain the height of elements to a certain range. Two properties offer this functionality:
| Value: | <length> | <percentage> | inherit |
| Initial: | 0 |
| Applies to: | all elements |
| Inherited: | no |
| Percentages: | |
| Media: | visual |
| Computed value: | the percentage as specified or the absolute length |
| Value: | <length> | <percentage> | none | inherit |
| Initial: | none |
| Applies to: | all elements |
| Inherited: | no |
| Percentages: | |
| Media: | visual |
| Computed value: | the percentage as specified or the absolute length or 'none' |
These two properties allow authors to constrain box heights to a certain range. Values have the following meanings:
Negative values for 'min-height' and 'max-height' are illegal.
The following algorithm describes how the two properties influence the computed value of the 'height' property:
However, for replaced elements with both 'width' and 'height' computed as 'auto', 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.
As described in the section on inline formatting contexts, user agents flow inline boxes into a vertical stack of line boxes. The height of a line box is determined as follows:
Empty inline elements generate empty inline boxes, but these boxes
still have margins, padding, borders and a line height, and thus
influence these calculations just like elements with content. Note that if all the boxes in the line box are aligned along their bottoms, the line box will be exactly the height of the tallest box. If, however, the boxes are aligned along a common baseline, the line box top and bottom may not touch the top and bottom of the tallest box.just like elements with content.
Since the heightvalue of an inline box'line-height' may be different
from the font sizeheight of text inthe box (e.g., 'line-height' > 1em),content area there may be space above and below
rendered glyphs. The difference between the font sizecontent height and the computedused
value of 'line-height' is
called the leading. Half the leading is called
the half-leading.
User agents center glyphs vertically in an inline box, adding
half-leading on the top and bottom. For example, if a piece of text
is '12pt''12px' high and the 'line-height' value is '14pt', 2pts'14px',
2pxs of extra space should be added: 1pt1px above and 1pt1px below the
letters. (This applies to empty boxes as well, as if the empty box
contained an infinitelyinfinitesimally narrow letter.)
When the 'line-height'
value is less than the font size,content height, the final inline box height will be
less than the font size and the rendered glyphs will "bleed" outside
the box. If such a box touches the edge of a line box, the rendered
glyphs will also "bleed" into the adjacentadjoining line box.
Although margins, borders, and padding of non-replaced elements do
not enter into inline box height calculation (and thusthe line box calculation),calculation, they are still rendered
around inline boxes. This means that if the height of a line boxspecified by 'line-height' is shorterless than the
outer edgescontent height of the boxes it contains,contained boxes, backgrounds and colors of padding
and borders may "bleed" into adjacentadjoining line boxes. However, in this case, someUser agents may useshould
render the line boxboxes in document order. This will cause the borders on
subsequent lines to "clip"paint over the borderborders and padding areas (i.e., not render them).text of previous lines.
| Value: | normal | <number> | <length> | <percentage> | inherit |
| Initial: | normal |
| Applies to: | all elements |
| Inherited: | yes |
| Percentages: | refer to the font size of the element itself |
| Media: | visual |
| | for <length> and <percentage> the |
On a block-level, table-cell, table-caption or inline-block element whose content
is composed of inline-level
elements, it'line-height' specifies the minimal height of line boxes
within the element. The minimum height consists of a minimum height above
the block's baseline and a minimum depth below it, exactly as if each
generatedline box starts with a zero-width inline box. Ifbox with the
property is setblock's font and line height properties (what TEX calls a
"strut").
On an inline-level element, it'line-height'
specifies the exactheight that is used in the calculation of each box generated bythe element.line box
height (except for inline replaced elements, where the
height of the box is given by the 'height' property.)property).
Values for this property have the following meanings:
The three rules in the example below have the same resultant line height:
div { line-height: 1.2; font-size: 10pt } /* number */
div { line-height: 1.2em; font-size: 10pt } /* length */
div { line-height: 120%; font-size: 10pt } /* percentage */
When an element contains text that is rendered
in more than one font, user agents shouldmay determine the 'line-height' value according to
the largest font size.
Generally, when there is only one value of 'line-height' for all inline
boxes in a paragraph (and no tall images), the above will ensure that baselines of successive lines are exactly 'line-height' apart. This is important when columns of text in different fonts have to be aligned, for example in a table. Note that replaced elements have a 'font-size' and a 'line-height' property, even if they are not used directly to determine the height of the box. The 'font-size' is, however, used to define the 'em' and 'ex' units, andimages), the above will ensure that
baselines of successive lines are exactly 'line-height' has a roleapart. This is
important when columns of text in the 'vertical-align' property.different fonts have to be aligned,
for example in a table.
| Value: | baseline | sub | super | top | text-top | middle | bottom | text-bottom | <percentage> | <length> | inherit |
| Initial: | baseline |
| Applies to: | inline-level and 'table-cell' elements |
| Inherited: | no |
| Percentages: | refer to the 'line-height' of the element itself |
| Media: | visual |
| Computed value: | for <percentage> and <length> the absolute length, otherwise as specified |
This property affects the vertical positioning inside a line box of the boxes generated by an inline-level element.
The following values only have meaning with respect to a parent inline-level element, or to a parent block-level element, if that element generates anonymous inline boxes ; they have no effect if no such parent exists.Note. Values of this property have
slightly different meanings in the context of tables.
Please consult the section on
table height algorithms for details.
The following values only have meaning with respect to a parent inline-level element, or to the strut of a parent block-level, table-cell, table-caption or inline-block element.
The remainingfollowing values referalign the element relative to the line boxbox.
Since the element may have children aligned relative to it (which in
whichturn may have descendants aligned relative to them), these values use
the generated box appears:bounds of the aligned subtree. The aligned subtree of
an inline element contains that element and the aligned subtrees of
all children inline elements whose computed 'vertical-align' value is
not 'top' or 'bottom'. The top of the aligned subtree is the highest
of the tops of the boxes in the subtree, and the bottom is analogous.
The baseline of an 'inline-table' is the baseline of the first row of the table.
The baseline of an 'inline-block' is the baseline of its last line box in the normal flow, unless it has either no in-flow line boxes or if its 'overflow' property has a computed value other than 'visible', in which case the baseline is the bottom margin edge.