<inset-area>

<inset-area> = [
  [ left | center | right | span-left | span-right | x-start | x-end | span-x-start | span-x-end | x-self-start | x-self-end | span-x-self-start | span-x-self-end | span-all ]
||
  [ top | center | bottom | span-top | span-bottom | y-start | y-end | span-y-start | span-y-end | y-self-start | y-self-end | span-y-self-start | span-y-self-end | span-all ]
|
  [ block-start | center | block-end | span-block-start | span-block-end | span-all ]
||
  [ inline-start | center | inline-end | span-inline-start | span-inline-end | span-all ]
|
  [ self-block-start | self-block-end | span-self-block-start | span-self-block-end | span-all ]
||
  [ self-inline-start | self-inline-end | span-self-inline-start | span-self-inline-end | span-all ]
|
  [ start | center | end | span-start | span-end | span-all ]{1,2}
|
  [ self-start | center | self-end | span-self-start | span-self-end | span-all ]{1,2}
]

Inset areas work on the concept of an inset-area grid, a 3x3 grid of tiles composed of four grid lines, two on each axis, with an anchor element being the center tile:

When used as the value of a positioned elements inset-area property, the dimensions of the center tile are defined by the containing block of the element's default anchor element. The dimensions of the grid's outer edge are defined by the positioned element's containing block. Logical keyterms are generally based on the writing mode and direction of the containing block, except for the self-* keyterms, which are calculated from the writing mode of the anchor-positioned element.

The grid tiles are broken up into rows and columns:

• The three rows are represented by the physical values top, center, and bottom. They also have logical equivalents such as block-start, center, and block-end, and coordinate equivalents — y-start, center, and y-end.
• The three columns are represented by the physical values left, center, and right. They also have logical equivalents such as inline-start, center, and inline-end, and coordinate equivalents — x-start, center, and x-end.

<inset-area> values contain one or two keywords defining a specific area of the inset-area grid. Setting an <inset-area> value on a positioned element's inset-area property places its containing block in the specified grid area:

/* Examples: Two keywords to place the element in a single specific tile */
inset-area: top left;
inset-area: bottom right;
inset-area: start end;
inset-area: center end;
inset-area: block-start center;
inset-area: inline-start block-end;
inset-area: x-start y-end;
inset-area: center y-self-end;

/* Examples: Two keywords to span the element across two tiles */
inset-area: top span-left;
inset-area: span-bottom right;
inset-area: center span-start;
inset-area: inline-start span-block-end;
inset-area: y-start span-x-end;

/* Examples: Two keywords to span the element across three tiles */
inset-area: top span-all;
inset-area: block-end span-all;
inset-area: x-self-start span-all;

/* Examples: One keyword with an implicit second keyword  */
inset-area: top; /* equiv: top span-all */
inset-area: inline-start; /* equiv: inline-start span-all */
inset-area: center; /* equiv: center center */
inset-area: span-all; /* equiv: center center */
inset-area: start; /* equiv: start start */
inset-area: end; /* equiv: end end */

The different types of keywords that can be used include:

• Physical grid keywords
• Generic logical row and column keywords
• Explicit inline and block logical keywords
• Coordinate grid keywords

The physical grid keywords specify a cell or section of the inset-area grid using physical values. These values are not affected by writing-mode or direction settings.

With physical row and column keywords, you can specify one keyword from each of the two lists below to select a single specific grid tile:

• top, center, or bottom: The top, center, or bottom row of the grid.
• left, center, or right: The left-hand, center, or right-hand column of the grid.

For example, top left selects the top left tile, while center right selects the center tile of the right-hand column.

The physical spanning keywords — when combined with a physical row or column keyword — specify a second grid tile for the inset area to expand into. When such a combination is set as an inset-area property value, a selected element is initially placed in the center of the specified row or column; it then spans in the direction specified in the spanning keyword, spanning two grid tiles:

span-left

Span the center column and the left-hand column of the grid.

span-right

Span the center column and the right-hand column of the grid.

span-top

Span the center row and the top row of the grid.

span-bottom

Span the center row and the bottom row of the grid.

span-all

Valid with all the keyword types, spans the cell listed as well as the adjacent cells in the same row or column. See span-all below.

For example, top span-left spans the top-center and top-left grid cells.

If only a single physical keyword is specified in the inset-area value, the other value is implied as follows:

left, right, top, or bottom

The other value defaults to span-all, causing the element to span all three tiles of the grid or row it was initially placed in. For example, left is equivalent to left span-all.

center, span-left, span-right, span-top, or span-bottom

The other value defaults to center. For example, span-left is equivalent to center span-left and center is equivalent to center center.

The logical grid keywords specify an area of the inset area grid using logical values. With these values, the position and direction are affected by writing-mode and direction settings on either the element's containing block or, in the case of the self keywords, the positioned element itself. There are two types of logical keywords; generic and explicit.

The generic logical keywords use the same terms for inline and block directions, with the direction determined by the position of the keyterm within a pair of <inset-area> values. The first value in a pair of values defines the block direction position and the second value defines the inline value. You can specify one or two keyterms from the following list. Specifying two from this list defines a single specific grid tile. The keyword position or direction is:

start

The start of the grid's block or inline direction, calculated from the containing block's writing mode.

end

The end of the grid's block or inline direction, calculated from the containing block's writing mode.

self-start

The start of the grid's block or inline direction, calculated from the element's own writing mode.

self-end

The end of the grid's block or inline direction, calculated from the element's own writing mode.

center

The center of the grid's block or inline direction, depending on whether this keyword is first or second, respectively.

For example, start end and self-start self-end both describe the position at the start of the block direction and the end of the inline direction. With writing-mode: horizontal-tb set, this is the top right of the anchor element, whereas with writing-mode: vertical-rl it is the bottom right of the anchor.

Spanning generic logical row and column keywords

The generic logical spanning keywords — when combined with a logical row or column keyword — specify a second grid tile for the inset area to expand into. When such a combination is set as an inset-area property value, a selected element is initially placed in the center of the specified row or column, and it then spans in the direction specified in the spanning keyword, spanning two grid tiles:

span-start

Span the center tile and the start tile of the grid row/column, with the direction refering to the writing mode of the element's containing block.

span-end

Span the center tile and the end tile of the grid row/column, with the direction refering to the writing mode of the element's containing block.

span-self-start

Span the center tile and the start tile of the grid row/column for the positioned element's own writing mode.

span-self-end

Span the center tile and the end tile of the grid row/column, calculated from the element's own writing mode.

For example, start span-end and self-start span-self-end both specify a grid inset area that starts in the center of the start block row, and spans across the tiles in that row that are also in the inline center and end columns. With writing-mode: horizontal-tb set, this would span over the top center and top right of the anchor, whereas with writing-mode: vertical-rl set it would span the element over the right center and bottom right.

The explicit inline and block logical row and column keywords refer explicitly to a block (row) or inline (column) position. You can specify one keyword for the block direction and one for the inline direction to select a single specific grid tile. Unlike with generic logical keyword values, the keyword order doesn't matter. However, declaring two keywords in the same axis invalidates the value.

block-start

The start of the grid's block direction calculated from the containing block's writing mode.

block-end

The end of the grid's block direction calculated from the containing block's writing mode.

inline-start

The start of the grid's inline direction calculated from the containing block's writing mode.

inline-end

The end of the grid's inline direction calculated from the containing block's writing mode.

For example, block-start inline-end specifies the tile at the start of the block direction and the end of the inline direction. With writing-mode: horizontal-tb set, this would be the tile at the top-right of the anchor, whereas with writing-mode: vertical-rl set this would be the tile at the bottom-right.

Spanning explicit inline and block logical keywords

The generic logical spanning keywords — when combined with a logical row or column keyword — specify a second grid tile for the inset area to expand into. When such a combination is set as an inset-area property value, a selected element is initially placed in the center of the specified row or column, based on the containing block's writing mode, and it then spans in the direction specified in the spanning keyword, spanning two grid tiles:

span-block-start

Span the center tile and the block-start tile of the specified inline column.

span-block-end

Span the center tile and the block-end tile of the specified inline column.

span-inline-start

Span the center tile and the inline-start tile of the specified block row.

span-inline-end

Span the center tile and the inline-end tile of the specified block row.

For example, block-end span-inline-start selects the center tile of the end block row and spans across the tiles in that row that are in the inline center and start columns. With writing-mode: horizontal-tb set, this would span the bottom-center and bottom-left grid tiles, whereas with writing-mode: vertical-rl set it would span the left-center and top-left grid tiles.

If only a single logical <inset-area> keyword is specified, the other value is implied as follows:

start, end, self-start, or self-end

The other value defaults to the same as the first value, selecting the grid cell at the start row and column, or the end row and column.

span-start, span-self-start, span-end, span-self-end

The other value defaults to center. For example, span-start is equivalent to span-start center.

block-start, block-end, inline-start, inline-end

The other value defaults to span-all, spanning all three tiles of the column or row set. For example, block-start is equivalent to block-start span-all.

span-block-start, span-block-end, span-inline-start, span-inline-end

The other value defaults to center. For example, span-inline-start is equivalent to span-inline-start center.

These keywords specify the cells of the inset-area grid using x- and y-coordinate values. Its position/direction will be affected by writing-mode and/or direction settings on either an element's containing block or, in the case of the self keywords, the element itself.

However, the grid cells are defined according to physical axes rather than block/inline directions:

• For writing-mode: horizontal-tb and vertical-lr, the x-axis runs left-to-right and the y-axis runs top-to-bottom.
• For writing-mode: horizontal-tb; direction: rtl and writing-mode: vertical-rl, the x-axis runs right-to-left and the y-axis runs top-to-bottom.

With coordinate row and column keywords, you can specify one keyword from the x-axis and one from the y-axis to define a single specific grid tile.

The x-axis keywords include:

x-start

The start tile along the grid's x-axis, calculated from the containing block's writing mode.

x-end

The end tile along the grid's x-axis, calculated from the containing block's writing mode.

x-self-start

The start tile along the grid's x-axis, calculated from the element's own writing mode.

x-self-end

The end tile along the grid's x-axis, calculated from the element's own writing mode.

center

The center of the grid's x-axis, calculated from the element's own writing mode.

The y-axis keywords include:

y-start

The start tile along the grid's y-axis, calculated from the containing block's writing mode.

y-end

The end tile along the grid's y-axis, calculated from the containing block's writing mode.

y-self-start

The start tile along the grid's y-axis, calculated from the element's own writing mode.

y-self-end

The end tile along the grid's y-axis, calculated from the element's own writing mode.

center

The center of the grid's y-axis, calculated from the element's own writing mode.

For example, x-end y-start and x-self-end y-self-start both select the grid cell at end of the x-axis and the start of the y-axis. With writing-mode: horizontal-tb set, this would be the cell to the top right of the anchor, whereas with writing-mode: vertical-rl is at the top left.

When combined with a coordinate row or column keyword, the coordinate-spanning keywords specify a second grid tile for the inset area to expand into. When such a combination is set as an inset-area property value, a selected element is initially placed in the center of the specified row or column, and it then spans in the direction specified in the spanning keyword, spanning two grid tiles:

span-x-start

Span the center tile and the x-start tile of the specified y-axis row.

span-x-end

Span the center tile and the x-end tile of the specified y-axis row.

span-y-start

Span the center tile and the y-start tile of the specified x-axis column.

span-y-end

Span the center tile and the y-end tile of the specified x-axis column.

For example, y-end span-x-end selects the tile at the center of the end y-row, and spans across the tiles in that row that are also in the x-center and x-end columns. With writing-mode: horizontal-tb set, the inset grid area would span the grid tiles at the bottom-center and bottom-right, whereas with writing-mode: vertical-rl set it would span the bottom-center and bottom-left tiles.

If only a single coordinate grid <inset-area> keyword is specified, the other value is implied as follows:

x-start, x-self-start, x-end, x-self-end, y-start, y-self-start, y-end, or y-self-end

The other value defaults to span-all, selecting the grid tiles spanning all three tiles of the column or row it was initially placed in. For example, x-start is equivalent to x-start span-all.

span-x-start, span-x-end, span-y-start, or span-y-end

The other value defaults to center. For example, span-start is equivalent to span-start center.

span-all is a special keyword usable with all of the row and column keywords listed in the sections above. When you specify two values — a row/column keyword and span-all, the element is placed in the specified row or column, and it then spans all of the tiles in that row or column.

See the inset-area property page.

For detailed information on anchor features and usage, see the CSS anchor positioning module landing page and the Using CSS anchor positioning guide.

• inset-area
• anchor-name
• position-anchor
• anchor() function
• Using CSS anchor positioning guide
• Handling overflow: try fallbacks and conditional hiding guide
• CSS anchor positioning module