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

Try it


/* Keyword values */
border-left-width: thin;
border-left-width: medium;
border-left-width: thick;

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

/* Global keywords */
border-left-width: inherit;
border-left-width: initial;
border-left-width: revert;
border-left-width: revert-layer;
border-left-width: unset;



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-left-style is none or hidden
Animation type a length

Formal syntax

border-left-width = 

<line-width> =
<length [0,∞]> |
thin |
medium |


Comparing border widths


<div>Element 1</div>
<div>Element 2</div>


div {
  border: 1px solid red;
  margin: 1em 0;

div:nth-child(1) {
  border-left-width: thick;
div:nth-child(2) {
  border-left-width: 2em;



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-left-width 1 12 1 4 3.5 1 2.2 18 4 10.1 1 1.0

See also

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