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

/* 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; 

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 # the-border-width

See also

The other border-width-related CSS properties: border-left-width, border-right-width, border-top-width, and border-width. The other border-bottom-related CSS properties: border, border-bottom, border-bottom-style, and border-bottom-color.

Last modified: Aug 12, 2021, by MDN contributors

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