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 value medium
Applies to all elements. It also applies to ::first-letter.
Inherited no
Media visual
Computed value the absolute length or 0 if border-left-style is none or hidden
Animation type a length
Canonical order the 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:
thin A thin border
medium A medium border
thick 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.


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

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