border-bottom-width property CSS Reference

Definition and Usage

The border-bottom-width CSS property sets the width of the bottom border of a box.

  • Initial medium
  • Applies to all elements
  • Inherited no
  • Media visual
  • Computed Value the absolute length or 0 if border-bottom-style is none or hidden
  • Animatable yes, as a length
  • Canonical order the unique non-ambiguous order defined by the formal grammar


Formal syntax: <br-width>
border-bottom-width: 10em    /* Any <length> value */
border-bottom-width: 3vmax
border-bottom-width: 6px
border-bottom-width: thin    /* A keyword */
border-bottom-width: medium
border-bottom-width: thick
border-right-width: inherit


Is either a non-negative explicit <length> value or a keyword denoting the thickness of the bottom border. The keyword must be one of the following values:
A thin border
A medium border
A thick border
The specification doesn't precisely define the thickness of each of the keywords, which is therefore implementation specific. Nevertheless, it requests that the thickness does follow the thin ≤ medium ≤ thick inequality and that the values are constant on a single document.
Represents the calculated value of the border-bottom-width of the parent's element.


element {
    border-bottom-width: thin;
    border-bottom-style: solid;
    border-bottom-color: #000;


Desktop browsers

FeatureChromeFirefox (Gecko)Internet ExplorerOperaSafari (WebKit)
Basic support1.01.0 (1.0) (85)

Mobile browsers

FeatureAndroidFirefox Mobile (Gecko)IE PhoneOpera MobileSafari Mobile
Basic supportNANANANANA

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