Web/CSS/border-bottom-width

The border-bottom-width CSS property sets the width of the bottom border of an element.

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Syntax

/* Keyword values */
border-bottom-width: thin;
border-bottom-width: medium;
border-bottom-width: thick;

/* <length> values */
border-bottom-width: 10em;
border-bottom-width: 3vmax;
border-bottom-width: 6px;

/* Global keywords */
border-bottom-width: inherit;
border-bottom-width: initial;
border-bottom-width: unset;

Values

<line-width>

Defines the width of the border, either as an explicit nonnegative <length> or a keyword. If it's a keyword, it must be one of the following values:

`thin`		A thin border
`medium`		A medium border
`thick`		A thick border

Note: Because the specification doesn't define the exact thickness denoted by each keyword, the precise result when using one of them is implementation-specific. Nevertheless, they always follow the pattern thin ≤ medium ≤ thick, and the values are constant within a single document.

Formal definition

Initial value	`medium`
Applies to	all elements. It also applies to `::first-letter`.
Inherited	no
Computed value	the absolute length or `0` if `border-bottom-style` is `none` or `hidden`
Animation type	a length

Formal syntax

<line-width>where <line-width> = <length> | thin | medium | thick

Examples

Comparing bottom border widths

HTML

<div>Element 1</div>
<div>Element 2</div>

CSS

div { 
  border: 1px solid red;
  margin: 1em 0;
}

div:nth-child(1) {
  border-bottom-width: thick;
}
div:nth-child(2) {
  border-bottom-width: 2em;
}

Result

Specifications

Specification	Status	Comment
CSS Backgrounds and Borders Module Level 3The definition of 'border-bottom-width' in that specification.	Candidate Recommendation	No significant change.
CSS Level 2 (Revision 1)The definition of 'border-bottom-width' in that specification.	Recommendation	No significant change.
CSS Level 1The definition of 'border-bottom-width' in that specification.	Recommendation	Initial definition.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`border-bottom-width`	Chrome Full support 1	Edge Full support 12	Firefox Full support 1	IE Full support 4	Opera Full support 3.5	Safari Full support 1	WebView Android Full support 2.3	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support 10.1	Safari iOS Full support 1	Samsung Internet Android Full support 1.0

Legend

Full support: Full support