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

/* Any <length> value */
border-left-width: 10em;
border-left-width: 3vmax;
border-left-width: 6px;

/* A keyword */
border-left-width: thin;
border-left-width: medium;
border-left-width: thick;

border-left-width: inherit;

Initial valuemedium
Applies toall elements. It also applies to ::first-letter.
Computed valuethe absolute length or 0 if border-left-style is none or hidden
Animation typea length
Canonical orderthe unique non-ambiguous order defined by the formal grammar



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

Formal syntax


<br-width> = <length> | thin | medium | thick


.left-red-border { 
  border-left-width: thin;
  border-left-style: solid;
  border-left-color: #F00;
  padding: 10px;
<div class="left-red-border">
  Example of a border on the left side.


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

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 1.0 (Yes) 1.0 (1.0) 4.0 3.5 1.0 (85)
Feature Android Edge Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support ? (Yes) ? ? ? ?

See also

Document Tags and Contributors

 Last updated by: elysdir1,