bottom - CSS: Cascading Style Sheets 编辑

The bottom CSS property participates in setting the vertical position of a positioned element. It has no effect on non-positioned elements.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

The effect of bottom depends on how the element is positioned (i.e., the value of the position property):

• When position is set to absolute or fixed, the bottom property specifies the distance between the element's bottom edge and the bottom edge of its containing block.
• When position is set to relative, the bottom property specifies the distance the element's bottom edge is moved above its normal position.
• When position is set to sticky, the bottom property is used to compute the sticky-constraint rectangle.
• When position is set to static, the bottom property has no effect.

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

Syntax

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

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

/* Keyword value */
bottom: auto;

/* Global values */
bottom: inherit;
bottom: initial;
bottom: unset;

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 distance that the element is moved above its normal position.

<percentage>

A <percentage> of the containing block's height.

auto

Specifies that:

• for absolutely positioned elements, the position of the element is based on the top property, while height: auto is treated as a height based on the content; or if top is also auto, the element is positioned where it should vertically be positioned if it were a static element.
• for relatively positioned elements, the distance of the element from its normal position is based on the top property; or if top is also auto, the element is not moved vertically at all.

inherit

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

Formal definition

Initial value	auto
Applies to	positioned elements
Inherited	no
Percentages	refer to the height of the containing block
Computed value	if specified as a length, the corresponding absolute length; if specified as a percentage, the specified value; otherwise, auto
Animation type	a length, percentage or calc();

Formal syntax

<length> | <percentage> | auto

Examples

Absolute and fixed positioning

This example demonstrates the difference in behavior of the bottom property, when position is absolute versus fixed.

HTML

<p>This<br>is<br>some<br>tall,<br>tall,<br>tall,<br>tall,<br>tall<br>content.</p>
<div class="fixed"><p>Fixed</p></div>
<div class="absolute"><p>Absolute</p></div>

CSS

p {
  font-size: 30px;
  line-height: 2em;
}

div {
  width: 48%;
  text-align: center;
  background: rgba(55,55,55,.2);
  border: 1px solid blue;
}

.absolute {
  position: absolute;
  bottom: 0;
  left: 0;
}

.fixed {
  position: fixed;
  bottom: 0;
  right: 0;
}

Result

Specifications

Specification	Status	Comment
CSS Positioned Layout Module Level 3 The definition of 'bottom' in that specification.	Working Draft	Adds behavior for sticky positioning.
CSS Level 2 (Revision 1) The definition of 'bottom' in that specification.	Recommendation	Initial definition.

Browser compatibility

BCD tables only load in the browser

See also

• inset, the shorthand for all related properties: top, bottom, left, and right
• The mapped logical properties: inset-block-start, inset-block-end, inset-inline-start, and inset-inline-end and the shorthands inset-block and inset-inline
• position