bottom

Summary

The bottom CSS property participates in specifying the position of positioned elements.

For absolutely positioned elements, that is, those whose position property is set to absolute or fixed, the bottom property specifies the distance between the bottom margin edge of the element and the bottom edge of the block containing the element.

For relatively positioned elements, that is, those with whose position property is set to relative, the bottom property specifies the distance the element's bottom edge is moved above its normal position.

When both top and bottom are specified, and height is unspecified or either auto or 100%, both the top and bottom distances are respected. In all other situations, if height is constrained in any way, the top property takes precedence and the bottom property is ignored.

Initial value	`auto`
Applies to	positioned elements
Inherited	no
Percentages	refer to the height of the containing block
Media	visual
Computed value	if specified as a length, the corresponding absolute length; if specified as a percentage, the specified value; otherwise, `auto`
Animatable	yes, as a length, percentage or calc(); when both values are lengths, they are interpolated as lengths; when both values are percentages, they are interpolated as percentages; otherwise, both values are converted into a `calc()` function that is the sum of a length and a percentage (each possibly zero), and these `calc()` functions have each half interpolated as real numbers.
Canonical order	the unique non-ambiguous order defined by the formal grammar

Syntax

/* <length> values */
bottom: 3px;
bottom: 2.4em;

/* <percentages> of the height of the containing block */
bottom: 10%;

/* keyword values */
bottom: auto;
bottom: inherit;

Values

<length>

A negative, null, or positive <length> that represents:

for absolutely positioned elements, the distance to the bottom edge of the containing block;
for relatively positioned elements, the offset that the element is moved above its position in the normal flow if it wasn't positioned.

<percentage>

A <percentage> of the containing block's height, used as described in the summary.

auto

Specifies that:

for absolutely positioned elements, the position of the element is based on the top property, and height: auto is treated as a height based on the content.
for relatively positioned elements, the offset the element from its original position is based on the top property, or if top is also auto, the element is not moved vertically at all.

inherit

Indicates that the value is the same as the computed value from its parent element (which may not be its containing block). This computed value is then handled as if it were a <length>, <percentage>, or the auto keyword.

Formal syntax

<length> | <percentage> | auto

Examples

element { 
    position: absolute;
    bottom: 20px; 
    height: 200px;
    border: 1px solid #000;
}

The following sample demonstrates the difference in behavior of the bottom property when position is absolute versus fixed. When the regular text becomes taller than the viewable portion of the page (that is, the browser window's viewport), blocks positioned with position:absolute scroll with the page, while blocks positioned with position:fixed don't.

<!DOCTYPE html>
<html>
<head>
<title>Position at bottom, absolute or fixed</title>
<style type="text/css">
p {font-size:30px; line-height:3em;}
div.pos {width:49%; text-align:center; border:2px solid #00f;}
div#abs {position:absolute; bottom:0; left:0;}
div#fix {position:fixed; bottom:0; right:0;}
</style>
</head>
<body>
  <p>This<br>is<br>some<br>tall,<br>tall,
    <br>tall,<br>tall,<br>tall<br>content.</p>
  <div id="fix" class="pos"><p>Fixed</p></div>
  <div id="abs" class="pos"><p>Absolute</p></div>
</body>
</html>

Specifications

Specification	Status	Comment
CSS Level 2 (Revision 1) The definition of 'bottom' in that specification.	Recommendation	Initial definition

Feature	Chrome	Firefox (Gecko)	Internet Explorer	Opera	Safari (WebKit)
Basic support	1.0	1.0 (1.7 or earlier)	5^[1]	6	1.0 (85)

Feature	Android	Firefox Mobile (Gecko)	IE Phone	Opera Mobile	Safari Mobile
Basic support	?	1.0 (1.9.2)	?	?	?

[1] In Internet Explorer versions before 7.0, when both top and bottom are specified, the element position is over-constrained and the top property has precedence. In that case the computed value of bottom is set to -top, while its specified value is ignored.