CSS border-left-width Property

The border-left-width property is used to define the width of an element’s left border.

The width of the left border, as well as all the other border sides, can also be defined with the border or border-width shorthand properties.

For setting the border-left-width you should first define the border-style property, because you need borders before setting its width. You can use either border-left-style or border-style CSS properties to define the border-style.

The specification doesn't define the exact thickness of each keyword. However, they always follow this order: thin ≤ medium ≤ thick.

The specification does not define how borders of different width and styles connect in the corners.

Initial Value	medium
Applies to	All elements. It also applies to ::first-letter.
Inherited	No
Animatable	Yes. The width of the border is animatable.
Version	CSS1
DOM Syntax	object.style.borderLeftWidth = "4px";

Syntax

border-left-width: medium | thin | thick | length | initial | inherit;

Example of the border-left-width property with the "thick" value:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      p {
        padding: 10px;
        border-style: dashed;
        border-left-width: thick;
      }
    </style>
  </head>
  <body>
    <h2>Border-left-width example</h2>
    <p>As you can see the width of the left border is set to thick.</p>
  </body>
</html>

Try it Yourself »

Example of the border-left-width property with all the values:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      body {
        background: #ccc;
        font-size: 20px;
        text-align: center;
      }
      main div {
        display: flex;
        align-items: center;
        justify-content: center;
        color: black;
        padding-top: 30px;
        padding-bottom: 30px;
        width: 200px;
        height: 100px;
        margin: 15px;
        font-weight: bold;
        border: solid;
      }
      .flex-center {
        display: flex;
        justify-content: center;
      }
      /* border-left-width example classes */
      .b1 {
        border-left-width: medium;
      }
      .b2 {
        border-left-width: thin;
      }
      .b3 {
        border-left-width: thick;
      }
      .b4 {
        border-left-width: 10px;
      }
      .b5 {
        border-left-width: initial;
      }
      .b6 {
        border-left-width: inherit;
      }
    </style>
  </head>
  <body>
    <h1>Border-left-width value examples</h1>
    <main class="flex-center">
      <div class="b1">
        medium
      </div>
      <div class="b2">
        thin
      </div>
      <div class="b3">
        thick
      </div>
    </main>
    <main class="flex-center">
      <div class="b4">
        10px length
      </div>
      <div class="b5">
        initial
      </div>
      <div class="b6">
        inherit
      </div>
    </main>
  </body>
</html>

Try it Yourself »

Result

Values

Value	Description	Play it
medium	Defines medium left border. It is the default value of this property.	Play it »
thin	Defines a thin left border. It is up to the user agent to determine the exact width.	Play it »
thick	Defines a thick left border. It is up to the user agent to determine the exact width.	Play it »
length	Defines the the thickness length of the left border. For example, 10px, 5em, 8pt, etc.	Play it »
initial	Sets the property to its default value.	Play it »
inherit	Inherits the property from its parent element.