<position> - CSS: Cascading Style Sheets 编辑

The <position> (or <bg-position>) CSS data type denotes a two-dimensional coordinate used to set a location relative to an element box. It is used in the background-position and offset-anchor properties.

Note: The final position described by the <position> value does not need to be inside the element's box.

Syntax

The <position> data type is specified with one or two keywords, with optional offsets.

The keyword values are center, top, right, bottom, and left. Each keyword represents either an edge of the element's box or the center line between two edges. Depending on the context, center represents either the center between the left and right edges, or the center between the top and bottom edges.

If specified, an offset can be either a relative <percentage> value or an absolute <length> value. Positive values are offset towards the right or the bottom, whichever is appropriate. Negative values are offset in the opposite directions.

If only a single offset value is specified, it defines the x-coordinate, with the value for the other axis defaulting to center.

/* 1-value syntax */
keyword                  /* Either the horizontal or vertical position; the other axis defaults to center */
value                    /* The position on the x-axis; the y-axis defaults to 50% */

/* 2-value syntax */
keyword keyword          /* A keyword for each direction (the order is irrelevant) */
keyword value            /* A keyword for horizontal position, value for vertical position */
value keyword            /* A value for horizontal position, keyword for vertical position */
value value              /* A value for each direction (horizontal then vertical) */

/* 4-value syntax */
keyword value keyword value /* Each value is an offset from the keyword that preceeds it */

Formal syntax

[
 [ left | center | right ] || [ top | center | bottom ]
|
 [ left | center | right | <length> | <percentage> ]
 [ top | center | bottom | <length> | <percentage> ]?
|
 [ [ left | right ] [ <length> | <percentage> ] ] &&
 [ [ top | bottom ] [ <length> | <percentage> ] ]
]

Note: The background-position property also accepts a three-value syntax. This is not allowed in other properties that use <position>.

Interpolation

When animated, a point's abscissa and ordinate values are interpolated independently. However, because the speed of the interpolation is determined by a single timing function for both coordinates, the point will move in a straight line.

Examples

Valid positions

center
left
center top

right 8.5%
bottom 12vmin right -6px

10% 20%
8rem 14px

Invalid positions

left right
bottom top
10px 15px 20px 15px

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• CSS Values and Units
• CSS Values and Units introduction
• background-position
• radial-gradient()
• conic-gradient()