border-bottom-width

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

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: revert;
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
medium
thick

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
CSS Backgrounds and Borders Module Level 4 (CSS Backgrounds and Borders 4) # the-border-width

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`border-bottom-width`	1	12	1	4	3.5	1	2.2	18	4	10.1	1	1.0