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<h1>CSS Grid Layout Module Level 1</h1>
<pre class='metadata'>
Status: ED
Shortname: css-grid
Level: 1
Group: csswg
ED: http://dev.w3.org/csswg/css-grid/
TR: http://www.w3.org/TR/css-grid-1/
Previous version: http://www.w3.org/TR/2014/WD-css-grid-1-20140513/
Previous version: http://www.w3.org/TR/2014/WD-css-grid-1-20140123/
Previous version: http://www.w3.org/TR/2013/WD-css3-grid-layout-20130402/
Previous version: http://www.w3.org/TR/2012/WD-css3-grid-layout-20121106/
Editor: Tab Atkins Jr., Google, http://www.xanthir.com/contact/
Editor: fantasai, Mozilla, http://fantasai.inkedblade.net/contact
Editor: Rossen Atanassov, Microsoft, ratan@microsoft.com
Former editor: Alex Mogilevsky, Microsoft Corporation, alexmog@microsoft.com
Former editor: Phil Cupp, Microsoft Corporation, pcupp@microsoft.com
!Issues list: <a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=CSS&component=Grid+Layout&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED">In Bugzilla</a>
Abstract: This CSS module defines a two-dimensional grid-based layout system, optimized for user interface design. In the grid layout model, the children of a grid container can be positioned into arbitrary slots in a flexible or fixed predefined layout grid.
Ignored Terms: containing block, <positive-integer>, <ident>, auto, grid-*-start, grid-*-end, flex factor, flex factors, block formatting context, grid-auto-position
Link Defaults: css21 (property) margin, css-align-3 (dfn) alignment container/alignment subject
At Risk: the ''grid-template-rows/subgrid'' value of 'grid-template-columns' and 'grid-template-rows', and its component parts individually
</pre>
<style type="text/css">
.example {
clear:both
}
.pseudo-code {
font-family:monospace
}
.pseudo-code > ol {
list-style-type:decimal
}
.pseudo-code > ol > li > ol {
list-style-type:lower-latin
}
.pseudo-code > ol > li > ol > li > ol {
list-style-type:lower-roman
}
.pseudo-code ul {
list-style-type:disc
}
dd > p:nth-child(1) {
margin-top:0
}
dd:last-child {
margin-bottom: 0;
}
dl.phase {
padding-left: .5em;
border-left: .5em #e0e0e0 solid;
}
</style>
<h2 id='intro'>
Introduction and Overview</h2>
Grid layout contains features targeted at web application authors.
The grid can be used to achieve many different layouts.
It excels at dividing up space for major regions of an application,
or defining the relationship in terms of size, position, and layer
between parts of a control built from HTML primitives.
Like tables,
grid layout enables an author to align elements into columns and rows,
but unlike tables,
grid layout doesn't have content structure,
and thus enables a wide variety of layouts not possible with tables.
For example, the children of a grid container can position themselves
such that they overlap and layer similar to positioned elements.
In addition, the absence of content structure in grid layout helps to manage changes to layout
by using fluid and source order independent layout techniques.
By combining media queries with the CSS properties that control layout of the grid container and its children,
authors can adapt their layout to changes in device form factors, orientation, and available space,
without needing to alter the semantic nature of their content.
<h3 id='background'>
Background and Motivation</h3>
<figure class="sidefigure">
<img class="figure" alt="Image: Application layout example requiring horizontal and vertical alignment." src="images/basic-form.png" />
<figcaption>Application layout example requiring horizontal and vertical alignment.</figcaption>
</figure>
As websites evolved from simple documents into complex, interactive applications,
tools for document layout, e.g. floats,
were not necessarily well suited for application layout.
By using a combination of tables, JavaScript, or careful measurements on floated elements,
authors discovered workarounds to achieve desired layouts.
Layouts that adapted to the available space were often brittle
and resulted in counter-intuitive behavior as space became constrained.
As an alternative, authors of many web applications opted for a fixed layout
that cannot take advantage of changes in the available rendering space on a screen.
The capabilities of grid layout address these problems.
It provides a mechanism for authors to divide available space for layout into columns and rows
using a set of predictable sizing behaviors.
Authors can then precisely position and size the building block elements of their application
by into <a>grid areas</a> defined by these columns and rows.
Figure 1 illustrates a basic layout which can be achieved with grid layout.
<h3 id='adapting-to-available-space'>
Adapting Layouts to Available Space</h3>
<figure class="sidefigure">
<img alt="Image: Five grid items arranged according to content size and available space." src="images/game-smaller.png" />
<figcaption>Five grid items arranged according to content size and available space.</figcaption>
</figure>
<figure class="sidefigure">
<img alt="Image: Growth in the grid due to an increase in available space." src="images/game-larger.png" />
<figcaption>Growth in the grid due to an increase in available space.</figcaption>
</figure>
Grid layout can be used to intelligently reflow elements within a webpage.
Figure 2 represents a game with five major areas in the layout:
the game title, stats area, game board, score area, and control area.
The author's intent is to divide the space for the game such that:
<ul>
<li>
The stats area always appears immediately under the game title.
F328
<li>
The game board appears to the right of the stats and title.
<li>
The top of the game title and the game board should always align.
<li>
The bottom of the game board and the stats area align when the game has reached its minimum height,
but otherwise the game board will stretch to take advantage of all the screen real-estate available to it.
<li>
The score area should align into the column created by the game and stats area,
while the controls are centered under the board.
</ul>
As an alternative to using script to control the absolute position, width, and height of all elements,
the author can use grid layout,
as shown in Figure 3.
The following example shows how an author might achieve all the sizing, placement, and alignment rules declaratively.
Note that there are multiple ways to specify the structure of the grid
and to position and size <a>grid items</a>,
each optimized for different scenarios.
This example illustrates one that an author may use to define the position and space for each <a>grid item</a>
using the 'grid-template-rows' and 'grid-template-columns' properties on the <a>grid container</a>,
and the 'grid-row' and 'grid-column' properties on each <a>grid item</a>.
<pre class="example">
<style type="text/css">
#grid {
display: grid;
/* Two columns: the first sized to content, the second receives
* the remaining space, but is never smaller than the minimum
* size of the board or the game controls, which occupy this
* column. */
grid-template-columns: auto minmax(min-content, 1fr);
/* Three rows: the first and last sized to content, the middle
* row receives the remaining space, but is never smaller than
* the minimum height of the board or stats areas. */
grid-template-rows: auto minmax(min-content, 1fr) auto
}
/* Each part of the game is positioned between grid lines by
* referencing the starting grid line and then specifying, if more
* than one, the number of rows or columns spanned to determine
* the ending grid line, which establishes bounds for the part. */
#title { grid-column: 1; grid-row: 1 }
#score { grid-column: 1; grid-row: 3 }
#stats { grid-column: 1; grid-row: 2; justify-self: start }
#board { grid-column: 2; grid-row: 1 / span 2; }
#controls { grid-column: 2; grid-row: 3; align-self: center }
</style>
<div id="grid">
<div id="title">Game Title</div>
<div id="score">Score</div>
<div id="stats">Stats</div>
<div id="board">Board</div>
<div id="controls">Controls</div>
</div>
</pre>
<h3 id='source-independence'>
Source Independence</h3>
<figure class="sidefigure">
<img alt="Image: An arrangement suitable for portrait orientation." src="images/game-portrait.png" />
<figcaption>An arrangement suitable for ''portrait'' orientation.</figcaption>
</figure>
<figure class="sidefigure">
<img alt="Image: An arrangement suitable for landscape orientation." src="images/game-landscape.png" />
<figcaption>An arrangement suitable for ''landscape'' orientation.</figcaption>
</figure>
Continuing the prior example,
the author also wants the game to adapt to the space available on traditional computer monitors, handheld devices, or tablet computers.
Also, the game should optimize the placement of the components when viewed either in landscape or portrait orientation (Figures 4 and 5).
By combining grid layout with media queries,
the author is able to use the same semantic markup,
but rearrange the layout of elements independent of their source order,
to achieve the desired layout in both orientations.
The following example leverages grid layout’s ability to name the space which will be occupied by a <a>grid item</a>.
This allows the author to avoid rewriting rules for <a>grid items</a>
as the grid’s definition changes.
<pre class="example">
<style type="text/css">
@media (orientation: portrait) {
#grid {
display: grid;
/* The rows, columns and areas of the grid are defined visually
* using the grid-template-areas property. Each string is a row, and
* each word an area. The number of words in a string
* determines the number of columns. Note the number of words
* in each string must be identical. */
grid-template-areas: "title stats"
"score stats"
"board board"
"ctrls ctrls";
/* Columns and rows created with the template property can be
* assigned a sizing function with the grid-template-columns
* and grid-template-rows properties. */
grid-template-columns: auto minmax(min-content, 1fr);
grid-template-rows: auto auto minmax(min-content, 1fr) auto
}
}
@media (orientation: landscape) {
#grid {
display: grid;
/* Again the template property defines areas of the same name,
* but this time positioned differently to better suit a
* landscape orientation. */
grid-template-areas: "title board"
"stats board"
"score ctrls";
grid-template-columns: auto minmax(min-content, 1fr);
grid-template-rows: auto minmax(min-content, 1fr) auto
}
}
/* The grid-area property places a grid item into a named
* region (area) of the grid. */
#title { grid-area: title }
#score { grid-area: score }
#stats { grid-area: stats }
#board { grid-area: board }
#controls { grid-area: ctrls }
</style>
<div id="grid">
<div id="title">Game Title</div>
<div id="score">Score</div>
<div id="stats">Stats</div>
<div id="board">Board</div>
<div id="controls">Controls</div>
</div>
</pre>
<h3 id='grid-layering'>
Grid Layering of Elements</h3>
<figure class="sidefigure">
<img alt="Image: A control composed of layered HTML elements." src="images/control-layering-and-alignment.png" />
<figcaption>A control composed of layered HTML elements.</figcaption>
</figure>
In the example shown in Figure 6,
the author is creating a custom slider control.
The control has six parts.
The lower and upper labels align to the left and right edges of the control.
The track of the slider spans the area between the labels.
The lower and upper fill parts touch beneath the thumb,
and the thumb is a fixed width and height that can be moved along the track
by updating the two flex-sized columns.
Prior to the introduction of grid layout,
the author would have likely used absolute positioning to control the top and left coordinates,
along with the width and height of each HTML element that comprises the control.
By leveraging grid layout,
the author can instead limit script usage to handling mouse events on the thumb,
which snaps to various positions along the track
as the 'grid-template-columns' property of the <a>grid container</a> is updated.
<pre class="example">
<style type="text/css">
#grid {
display: grid;
/* The grid-template-columns and rows properties also support
* naming grid lines which can then be used to position grid
* items. The line names are assigned on either side of a column
* or row sizing function where the line would logically exist. */
grid-template-columns:
(start) auto
(track-start) 0.5fr
(thumb-start) auto
(fill-split) auto
(thumb-end) 0.5fr
(track-end) auto
(end);
}
/* The grid-placement properties accept named lines. Below the
* lines are referred to by name. Beyond any
* semantic advantage, the names also allow the author to avoid
* renumbering the grid-column-start and grid-row-start properties of the
* grid items. This is similar to the concept demonstrated in the
* prior example with the grid-template-areas property during orientation
* changes, but grid lines can also work with layered grid items
* that have overlapping areas of different shapes like the thumb
* and track parts in this example. */
#lower-label { grid-column-start: start }
#track { grid-column: track-start / track-end; align-self: center }
#upper-label { grid-column-end: end; }
/* Fill parts are drawn above the track so set z-index to 5. */
#lower-fill { grid-column: track-start / fill-split;
align-self: end;
z-index: 5 }
#upper-fill { grid-column: fill-split / track-end;
align-self: start;
z-index: 5 }
/* Thumb is the topmost part; assign it the highest z-index value. */
#thumb { grid-column: thumb-start / thumb-end; z-index: 10 }
</style>
<div id="grid">
<div id="lower-label">Lower Label</div>
<div id="upper-label">Upper Label</div>
<div id="track">Track</div>
<div id="lower-fill">Lower Fill</div>
<div id="upper-fill">Upper Fill</div>
<div id="thumb">Thumb</div>
</div>
</pre>
<h2 id='grid-concepts'>
Grid Layout Concepts and Terminology</h2>
In <dfn export>grid layout</dfn>,
the content of a <a>grid container</a> is laid out
by positioning and aligning it into a <a>grid</a>.
The <dfn export>grid</dfn> is an intersecting set of horizontal and vertical <a>grid lines</a>
that divides the <a>grid container</a>’s space into <a>grid areas</a>,
into which <a>grid items</a> (representing the <a>grid container</a>’s content) can be placed.
There are two sets of <a>grid lines</a>:
one set defining <dfn export title="grid column | column">columns</dfn>
that run along the <a href="http://www.w3.org/TR/css3-writing-modes/#block-axis-">block axis</a> (the <dfn export>column axis</dfn>),
and an orthogonal set defining <dfn export title="grid row | row">rows</dfn>
along the <a href="http://www.w3.org/TR/css3-writing-modes/#inline-axis-">inline axis</a> (the <dfn export>row axis</dfn>).
[[!CSS3-WRITING-MODES]]
<!--
<div class="figure">
<img class="figure" alt="Image: A diagram illustrating the relationship between the Grid Element and its Tracks, Lines, Areas and Items." src="images/grid-concepts.png" />
<p class="caption">A diagram illustrating the relationship between the <a>grid container</a> and its tracks, lines, areas and items.
</div>
-->
<figure>
<img class="figure" alt="Image: Grid Lines." src="images/grid-lines.png" />
<figcaption>Grid lines: Three in the block axis and four in the inline axis.</figcaption>
</figure>
<h3 id="grid-track-concept">
Grid Tracks and Cells</h3>
<dfn export>Grid track</dfn> is a generic term for a <a>grid column</a> or <a>grid row</a>—in
other words, it is the space between two adjacent <a>grid lines</a>.
Each <a>grid track</a> is assigned a sizing function,
which controls how wide or tall the column or row may grow,
and thus how far apart its bounding <a>grid lines</a> are.
A <dfn export>grid cell</dfn> is the similar term for the full grid—it
is the space between two adjacent row and two adjacent column <a>grid lines</a>.
It is the smallest unit of the grid that can be referenced when positioning <a>grid items</a>.
<div class="example">
In the following example there are two columns and three rows.
The first column is fixed at 150px.
The second column uses flexible sizing, which is a function of the unassigned space in the Grid,
and thus will vary as the width of the <a>grid container</a> changes.
If the used width of the <a>grid container</a> is 200px, then the second column 50px wide.
If the used width of the <a>grid container</a> is 100px, then the second column is 0px
and any content positioned in the column will overflow the <a>grid container</a>.
<pre>
<style type="text/css">
#grid {
display: grid;
grid-template-columns: 150px 1fr; /* two columns */
grid-template-rows: 50px 1fr 50px /* three rows */
}
</style>
</pre>
</div>
<h3 id="grid-line-concept">
Grid Lines</h3>
<dfn id='grid-line' export title='grid line|grid row line|grid column line'>Grid lines</dfn> are the horizontal and vertical dividing lines of the <a>grid</a>.
A <a>grid line</a> exists on either side of a column or row.
They can be referred to by numerical index,
or by an author-specified name.
A <a>grid item</a> references the <a>grid lines</a> to determine its position within the <a>grid</a>
using the <a href="#placement">grid-placement properties</a>.
<div class="example">
The following two examples create three column <a>grid lines</a> and four row <a>grid lines</a>.
The first example demonstrates how an author would position a <a>grid item</a> using <a>grid line</a> numbers.
The second example uses explicitly named <a>grid lines</a>.
<pre>
<style type="text/css">
#grid {
display: grid;
grid-template-columns: 150px 1fr;
grid-template-rows: 50px 1fr 50px
}
#item1 { grid-column: 2;
grid-row-start: 1; grid-row-end: 4; }
</style>
</pre>
<pre>
<style type="text/css">
/* equivalent layout to the prior example, but using named lines */
#grid {
display: grid;
grid-template-columns: 150px (item1-start) 1fr (item1-end);
grid-template-rows: (item1-start) 50px 1fr 50px (item1-end);
}
#item1 {
grid-column: item1-start / item1-end;
grid-row: item1-start / item1-end
}
</style>
</pre>
</div>
<h3 id="grid-area-concept">
Grid Areas</h3>
A <dfn export>grid area</dfn> is the logical space used to lay out one or more <a>grid items</a>.
It is bound by four <a>grid lines</a>, one on each side of the <a>grid area</a>,
and participates in the sizing of the <a>grid tracks</a> it intersects.
A <a>grid area</a> can be named explicitly using the 'grid-template-areas' property of the <a>grid container</a>,
or referenced implicitly by its bounding <a>grid lines</a>.
A <a>grid item</a> is assigned to a <a>grid area</a>
using the <a href="#placement">grid-placement properties</a>.
<div class="example">
<pre>
<style type="text/css">
/* using the template syntax */
#grid {
display: grid;
grid-template-areas: ". a"
"b a"
". a";
grid-template-columns: 150px 1fr;
grid-template-rows: 50px 1fr 50px
}
#item1 { grid-area: a }
#item2 { grid-area: b }
#item3 { grid-area: b }
/* Align items 2 and 3 at different points in the Grid Area "b". */
/* By default, Grid Items are stretched to fit their Grid Area */
/* and these items would layer one over the other. */
#item2 { align-self: start }
#item3 { justify-self: end; align-self: end }
</style>
</pre>
</div>
A <a>grid item</a>’s <a>grid area</a> forms the containing block into which it is laid out.
Percentage lengths specified on a <a>grid item</a> resolve against this containing block.
Percentages specified for 'margin-top', 'padding-top', 'margin-bottom', and 'padding-bottom' on a <a>grid item</a>
resolve against the height of its containing block,
rather than the width (as for blocks).
<a>Grid items</a> placed into the same <a>grid area</a> do not directly affect each other's layout.
Indirectly, a <a>grid item</a> can affect the position of a <a>grid line</a> in a column or row that uses a contents-based relative size,
which in turn can affect the position or size of another <a>grid item</a>.
<h2 id="grid-model">
Grid Containers</h2>
<h3 id='grid-containers'>
Establishing Grid Containers: the ''display/grid'' and ''inline-grid'' 'display' values</h3>
<pre class="propdef">
Name: display
New values: grid | inline-grid
</pre>
<dl dfn-for="display" dfn-type=value>
<dt><dfn>grid</dfn>
<dd>
This value causes an element to generate a block-level <a>grid container</a> box.
<dt><dfn>inline-grid</dfn>
<dd>
This value causes an element to generate an inline-level <a>grid container</a> box.
</dl>
A <dfn export>grid container</dfn> establishes a new <dfn export>grid formatting context</dfn> for its contents.
This is the same as establishing a block formatting context,
except that grid layout is used instead of block layout:
floats do not intrude into the grid container,
and the grid container's margins do not collapse with the margins of its contents.
<a>Grid containers</a> form a containing block for their contents
<a href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details">exactly like block containers do</a>. [[!CSS21]]
The 'overflow' property applies to <a>grid containers</a>.
Grid containers are not block containers,
and so some properties that were designed with the assumption of block layout
don't apply in the context of grid layout.
In particular:
<ul>
<li>
all of the 'column-*' properties in the Multicol module have no effect on a grid container.
<li>
'float' and 'clear' have no effect on a <a>grid item</a>.
(However, the 'float' property still affects the computed value of 'display' on children of a grid container,
as this occurs <em title=''>before</em> <a>grid items</a> are determined.)
<li>
'vertical-align' has no effect on a grid item.
<li>
the ''::first-line'' and ''::first-letter'' pseudo-elements do not apply to <a>grid containers</a>.
</ul>
If an element's specified 'display' is ''inline-grid''
and the element is floated or absolutely positioned,
the computed value of 'display' is <a value>grid</a>.
The table in <a href="http://www.w3.org/TR/CSS2/visuren.html#dis-pos-flo">CSS 2.1 Chapter 9.7</a> is thus amended
to contain an additional row,
with ''inline-grid'' in the "Specified Value" column
and <a>grid</a> in the "Computed Value" column.
<h3 id='intrinsic-sizes'>
Sizing Grid Containers</h3>
A <i>grid container</i> is sized
using the rules of the formatting context in which it participates.
As a block-level box in a <a>block formatting context</a>,
it is sized like any other block-level box that establishes a formatting context,
with an ''auto'' inline size calculated as for in-flow block boxes.
As an inline-level box in an inline formatting context,
it is sized as an atomic inline-level box (such as an inline-block).
In both inline and block formatting contexts,
the <i>grid container</i>’s ''auto'' block size is its max-content size.
<span class="issue">The block layout spec should define this?</span>
The <a>max-content size</a> of a <a>grid container</a> is
the sum of the <a>grid container’s</a> track sizes in the appropriate axis,
when the grid is sized under a <a>max-content constraint</a>.
The <a>min-content size</a> of a <a>grid container</a> is
the sum of the <a>grid container’s</a> track sizes in the appropriate axis,
when the grid is sized under a <a>min-content constraint</a>.
See [[!CSS3-SIZING]] for a definition of the terms in this section.
<h2 id="grid-items">
Grid Items</h2>
The contents of a <a>grid container</a> consists of zero or more <dfn export id="grid-item" title="grid item">grid items</dfn>:
each child of a <a>grid container</a>
becomes a <a>grid item</a>,
and each contiguous run of text that is directly contained inside a <a>grid container</a>
is wrapped in an anonymous <a>grid item</a>.
However, an anonymous grid item that contains only
<a href="http://www.w3.org/TR/CSS21/text.html#white-space-prop">white space</a>
is not rendered, as if it were ''display:none''.
A <a>grid item</a> establishes a new formatting context for its contents.
The type of this formatting context is determined by its 'display' value, as usual.
The computed 'display' of a <a>grid item</a>
is determined by applying the table in
<a href="http://www.w3.org/TR/CSS2/visuren.html#dis-pos-flo">CSS 2.1 Chapter 9.7</a>.
However, grid items are grid-level boxes, not block-level boxes:
they participate in their container's <a>grid formatting context</a>,
not in a block formatting context.
<div class="example">
Examples of grid items:
<pre>
<div style="display:grid">
<!-- grid item: block child -->
<div id="item1">block</div>
<!-- grid item: floated element; floating is ignored -->
<div id="item2" style="float: left;">float</div>
<!-- grid item: anonymous block box around inline content -->
anonymous item 3
<!-- grid item: inline child -->
<span>
item 4
<!-- grid items do not split around blocks -->
<div id=not-an-item>item 4</div>
item 4
</span>
</div></pre>
</div>
Some values of 'display' trigger the generation of anonymous boxes.
For example, a misparented ''table-cell'' child is fixed up
by <a href="http://www.w3.org/TR/CSS21/tables.html#anonymous-boxes">generating anonymous ''table'' and ''table-row'' elements</a> around it. [[!CSS21]]
This fixup must occur <em>before</em> a <a>grid container</a>’s children are promoted to <a>grid items</a>.
For example, given two contiguous child elements with ''display:table-cell'',
an anonymous table wrapper box around them becomes the <a>grid item</a>.
<p class='note'>
Future display types may generate anonymous containers (e.g. ruby) or otherwise mangle the box tree (e.g. run-ins).
It is intended that grid item determination run after these operations.
<!--
<h3 id="position-grid">
Non-children Grid Items</h3>
<p class="issue">
This is a proposal to create the ability to have descendants of a grid item participate in a grid layout,
similar to the behavior defined by the Template Layout module.
A descendant of the grid can be pulled out of flow and participate directly in the grid
by assigning it ''position: grid''.
An element with ''position: grid'' is pulled out of flow and participates as a grid item
belonging to the first ancestor with ''display: grid''.
If the element is positioned using named lines or slots,
it belongs to the first ancestor with ''display: grid'' that has all of the corresponding named lines/slots.
If no such ancestor exists, the item remains in flow.
<p class="issue">
Alternatively, the item can just go into the first grid,
and missing names are treated as <a value for="<grid-line>">auto</a>.
-->
<h3 id="visibility-collapse">
Collapsed Grid Items: the 'visibility' property</h3>
<p class='issue'>
We want the ability to collapse grid tracks
(similar to <a href="http://www.w3.org/TR/css3-flexbox/#visibility-collapse">collapsing flex items</a>
or <a href="http://www.w3.org/TR/CSS21/tables.html#dynamic-effects">table rows/columns</a>),
but we're not sure exactly how to do it.
Ideas welcome, please <a href="mailto:www-style@w3.org?Subject=%5Bcss-grid%5D%20Collapsing%20Grid%20Tracks">post them to www-style@w3.org</a>.
<h3 id='order-property'>
Reordered Grid Items: the 'order' property</h3>
The 'order' property also applies to <a>grid items</a>.
It affects their <a href="#grid-auto-flow-property">auto-placement</a> and <a href="#z-order">painting order</a>.
<h3 id="static-position">
Static Position of Grid Container Children</h3>
The <a href="http://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-width">static position</a> [[!CSS21]]
of an absolutely-positioned child of a <a>grid container</a>
is determined as if it were the sole grid item
in a fixed-size <i>grid area</i>
whose edges coincide with the padding edges of the <i>grid container</i>.
Note: Note that this position is affected by the values of 'justify-self' and 'align-self' on the child,
and that, as in most other layout models,
the absolutely-positioned child has no effect on the size of the containing block
or layout of its contents.
<h2 id='grid-definition'>
The Explicit Grid</h2>
The three properties 'grid-template-rows', 'grid-template-columns', and 'grid-template-areas'
together define the <dfn export>explicit grid</dfn> of a <a>grid container</a>.
The 'grid-template' property is a shorthand that sets all three at the same time.
The final grid may end up larger due to <a>grid items</a> placed outside the <a>explicit grid</a>;
in this case, any implicit tracks are sized by the 'grid-auto-rows' and 'grid-auto-columns' properties.
The size of the <a>explicit grid</a> is determined by the larger of
the number of rows/columns defined by 'grid-template-areas'
and the number of rows/columns sized by 'grid-template-rows'/'grid-template-columns'.
Any rows/columns defined by 'grid-template-areas' but not sized by 'grid-template-rows'/'grid-template-columns'
take their size from the 'grid-auto-rows'/'grid-auto-columns' properties.
Numeric indexes in the <a>grid-placement properties</a>
count from the edges of the <a>explicit grid</a>,
starting from 1.
Positive indexes count from the before/start side,
while negative indexes count from the after/end side.
<h3 id='track-sizing'>
Track Sizing: the 'grid-template-rows' and 'grid-template-columns' properties</h3>
<pre class='propdef'>
Name: grid-template-columns, grid-template-rows
Value: none | <<track-list>> | subgrid <<line-name-list>>?
Initial: none
Applies to: <a>grid containers</a>
Inherited: no
Percentages: refer to corresponding dimension of the content area
Media: visual
Computed value: As specified, except for ''grid-template-columns/auto'' (see prose), with lengths made absolute
</pre>
These properties specify,
as a space-separated <dfn export>track list</dfn>,
the line names and <a>track sizing functions</a> of the <a>grid</a>.
Each <dfn title="track sizing function|sizing function">track sizing function</dfn> can be specified as a length,
a percentage of the <a>grid container</a>’s size,
a measurement of the contents occupying the column or row,
or a fraction of the free space in the grid.
It can also be specified as a range using the ''minmax()'' notation,
which can combine any of the previously mentioned mechanisms
to specify separate <i title="min track sizing function">min</i>
and <i>max track sizing functions</i> for the column or row.
The 'grid-template-columns' property specifies the <a>track list</a> for the grid's columns,
while 'grid-template-rows' specifies the <a>track list</a> for the grid's rows.
The syntax of a <a>track list</a> is:
<pre>
<dfn><track-list></dfn> = [ <<line-names>>? [ <<track-size>> | <<repeat()>> ] ]+ <<line-names>>?
<dfn><track-size></dfn> = minmax( <<track-breadth>> , <<track-breadth>> ) | auto | <<track-breadth>>
<dfn><track-breadth></dfn> = <<length>> | <<percentage>> | <<flex>> | min-content | max-content
<dfn><line-names></dfn> = ( <<custom-ident>>* )
<dfn><line-name-list></dfn> = [ <<line-names>> | repeat(<<positive-integer>>, <<line-names>>+) ]+
</pre>
Where:
<dl dfn-for="grid-template-columns grid-template-rows" dfn-type=value>
<dt><dfn><<length>></dfn>
<dd>
A non-negative length, as defined by CSS3 Values. [[!CSS3VAL]]
<dt><dfn><<percentage>></dfn>
<dd>
A non-negative percentage, as defined by CSS3 Values. [[!CSS3VAL]]
<<percentage>> values are relative to the measure (logical width) of the <a>grid container</a> in column <a>grid tracks</a>,
and the extent (logical height) of the <a>grid container</a> in row <a>grid tracks</a>.
If the measure or extent of the <a>grid container</a> is an <a href="http://www.w3.org/TR/css3-sizing/#indefinite-size">indefinite size</a>,
<<percentage>> values relative to that size are treated as <a value for=width>auto</a>
(or, if in a ''minmax()'' function, as ''min-content'' when in the first position
and as ''max-content'' when in the second).
<dt><dfn><<flex>></dfn>
<dd>
A non-negative dimension with the unit ''fr'' specifying the track's <dfn noexport>flex factor</dfn>.
Each <<flex>>-sized track takes a share of the remaining space in proportion to its <i>flex factor</i>.
See <a href="#fr-unit">Flexible Lengths</a> for more details.
<dt><dfn>max-content</dfn>
<dd>
Represents the largest <i>max-content contribution</i>
of the <a>grid items</a> occupying the <a>grid track</a>.
<dt><dfn>min-content</dfn>
<dd>
Represents the largest <i>min-content contribution</i>
of the <a>grid items</a> occupying the <a>grid track</a>.
<dt><dfn title="minmax()">minmax(min, max)</dfn>
<dd>
Defines a size range
greater than or equal to <var>min</var>
and less than or equal to <var>max</var>.
If <var>max</var> < <var>min</var>,
then <var>max</var> is ignored and ''minmax(min,max)'' is treated as <var>min</var>.
As a maximum, a <<flex>> value sets the track's <i>flex factor</i>.
As a minimum, it is treated as zero
(or ''min-content'', if the <i>grid container</i> is sized under a <i>min-content constraint</i>).
<dt><dfn>auto</dfn>
<dd>
Computes to ''minmax(min-content, max-content)''.
</dl>
The <dfn value for="grid-template-rows grid-template-columns">none</dfn> value indicates that there is no <a>explicit grid</a>;
any rows/columns will be implicitly generated,
and their size will be determined by the 'grid-auto-rows' and 'grid-auto-columns' properties.
The <dfn value for="grid-template-rows grid-template-columns">subgrid</dfn> value indicates that the grid will align to its parent grid in that axis.
Rather than specifying the sizes of rows/columns explicitly,
they'll be taken from the parent grid's definition.
<div class='example'>
Given the following 'grid-template-columns' declaration:
<pre>grid-template-columns: 100px 1fr max-content minmax(min-content, 1fr);</pre>
Five grid lines are created:
<ol>
<li>
At the start edge of the <a>grid container</a>.
<li>
100px from the start edge of the <a>grid container</a>.
<li>
A distance from the previous line equal to half the <a>free space</a>
(the width of the <a>grid container</a>, minus the width of the non-flexible <a>grid tracks</a>).
<li>
A distance from the previous line equal to the maximum size of any <a>grid items</a>
belonging to the column between these two lines.
<li>
A distance from the previous line at least as large as the largest minimum size of any <a>grid items</a>
belonging to the column
288E
between these two lines,
but no larger than the other half of the <a>free space</a>.
</ol>
If the non-flexible sizes
(''100px'', ''max-content'', and ''min-content'')
sum to larger than the <a>grid container</a>’s width,
the final <a>grid line</a> will be a distance equal to their sum away from the start edge of the <a>grid container</a>
(the ''1fr'' sizes both resolve to ''0'').
If the sum is less than the <a>grid container</a>’s width,
the final <a>grid line</a> will be exactly at the end edge of the <a>grid container</a>.
This is true in general whenever there's at least one <<flex>> value among the <a>grid track</a> sizes.
</div>
<div class='example'>
Additional examples of valid <a>grid track</a> definitions:
<pre>
/* examples of valid track definitions */
grid-template-rows: 1fr minmax(min-content, 1fr);
grid-template-rows: 10px repeat(2, 1fr auto minmax(30%, 1fr));
grid-template-rows: calc(4em - 5px)
</pre>
</div>
<h4 id='named-lines'>
Named Grid Lines: the ''(<<custom-ident>>*)'' syntax</h4>
While <a>grid lines</a> can always be referred to by their numerical index,
<dfn export title="named line">named lines</dfn>
can make the <a>grid-placement properties</a> easier to understand and maintain.
Lines can be explicitly named in the 'grid-template-rows' and 'grid-template-columns' properties,
or <a href="#implicit-named-lines">implicitly named</a> by creating <a>named grid areas</a> with the 'grid-template-areas' property.
<div class='example'>
For example,
the following code gives meaningful names to all of the lines in the grid.
Note that some of the lines have multiple names.
<pre>
<style>
#grid {
display: grid;
grid-template-columns: (first nav) 150px (main) 1fr (last);
grid-template-rows: (first header) 50px (main) 1fr (footer) 50px (last);
}
</style>
</pre>
<figure class="figure">
<img class="figure" alt="Image: Named Grid Lines." src="images/grid-named-lines.png" />
<figcaption>Named Grid Lines.</figcaption>
</figure>
</div>
<h4 id='repeat-notation'>
Repeating Rows and Columns: the ''repeat()'' notation</h4>
The ''repeat()'' notation represents a repeated fragment of the <a>track list</a>.
This is just a syntactic shorthand that allows
writing a large number of columns or rows that exhibit a recurring pattern
in a more compact form.
The syntax of the ''repeat()'' notation is:
<pre class='prod'><dfn>repeat()</dfn> = repeat( <<positive-integer>> , [ <<line-names>>? <<track-size>> ]+ <<line-names>>? )</pre>
The first argument specifies the number of repetitions.
The second argument is a <a>track list</a>,
which is repeated that number of times.
The ''repeat()'' notation cannot be nested;
doing so makes the declaration invalid.
<div class='example'>
This example shows two equivalent ways of writing the same grid definition.
Both ways produce a grid with a single row and four "main" columns, each 250px wide,
surrounded by 10px "gutter" columns.
<pre>
<style>
#grid {
display: grid;
grid-template-columns: 10px (col-start) 250px (col-end)
10px (col-start) 250px (col-end)
10px (col-start) 250px (col-end)
10px (col-start) 250px (col-end) 10px;
grid-template-rows: 1fr;
}
/* Equivalent definition. */
#grid {
display: grid;
grid-template-columns: repeat(4, 10px (col-start) 250px (col-end)) 10px;
grid-template-rows: 1fr;
}
</style>
</pre>
</div>
If the ''repeat()'' function ends up placing two <<line-names>> adjacent to each other,
the name lists are merged.
For example, ''repeat(2, (a) 1fr (b))'' is equivalent to ''(a) 1fr (b a) 1fr (b)''.
Note: It is expected that a future level of this specification will define a value to be inserted between the repetitions,
similar to the argument of the <code>Array#join</code> method in JavaScript.
Implementations may cap the maximum number of repetitions they allow.
If they do so, they must support at least 10000 repetitions,
and if the number of repetitions is greater than the implementation's maximum,
the value must be capped to the implementation's maximum
(rather than being invalid, overflowing, or some other behavior).
<h4 id='fr-unit'>
Flexible Lengths: the ''fr'' unit</h4>
A <dfn export>flexible length</dfn> or <dfn><<flex>></dfn> is a dimension with the ''fr'' unit,
which represents a fraction of the <a>free space</a> in the <a>grid container</a>.
The distribution of <a>free space</a> occurs after all non-flexible <a>track sizing functions</a> have reached their maximum.
The total size of such rows or columns is subtracted from the available space, yielding the <a>free space</a>,
which is then divided among the flex-sized rows and columns in proportion to their <i>flex factor</i>.
Note: Flexible lengths in a <a>track list</a> work similarly to flexible lengths with a zero base size in [[CSS3-FLEXBOX]].
Each column or row's share of the <a>free space</a> can be computed as the column or row's
<code><flex> * <free space> / <sum of all <i>flex factors</i></code>.
For the purpose of this calculation,
a flexible length in the <var>min</var> position of a ''minmax()'' function is treated as ''0'' (an inflexible length).
When the available space is infinite
(which happens when the <a>grid container</a>’s width or height is <a>indefinite</a>),
flex-sized <a>grid tracks</a> are sized to their contents while retaining their respective proportions.
The used size of each flex-sized <a>grid track</a> is computed by
determining the ''max-content'' size of each flex-sized <a>grid track</a>
and dividing that size by the respective <i>flex factor</i>
to determine a “hypothetical ''1fr'' size”.
The maximum of those is used as the resolved ''1fr'' length (the <dfn>flex fraction</dfn>),
which is then multiplied by each <a>grid track</a>’s <i>flex factor</i> to determine its final size.
<h4 id="subgrids">
Subgrids: the ''grid-template-rows/subgrid'' keyword</h4>
A <a>grid item</a> can itself be a <a>grid container</a> by giving it ''display: grid'';
in this case the layout of its contents will be independent of the layout of the grid it participates in.
In some cases it might be necessary for the contents of multiple <a>grid items</a> to align to each other.
A <a>grid container</a> that is itself a <a>grid item</a>
can defer the definition of its rows or columns to its parent <a>grid container</a>
by using the ''grid-template-rows/subgrid'' keyword in 'grid-template-rows' and/or 'grid-template-columns',
making it a <dfn export>subgrid</dfn> in that dimension.
In this case, the <a>grid items</a> of the <a>subgrid</a>