CSS border-width

<!doctype html>
<title>Example</title>
<style>
div {
  font-size: 1.5em;
  padding: 20px;
  border-width: thin medium thick 30px;
  border-color: orange;
  border-style: solid;
  }
</style>
<div>This 'div' is styled using the CSS border-width property. Try changing the value to see the effect it has on the border width of each side of the div.</div>

The CSS border-width property is shorthand for setting the width of all borders on an element.

You can supply from one to four values. Each value specifies the width for each side of the element.

For example, if four values are provided, they will apply to the top, right, bottom and left borders - in that order. Supplying one value applies the width to all four sides. Supplying three values applies the styles to top, left and right, and bottom (in that order).

Syntax

Where

These values are explained below.

Possible Values

thin: Specifies a thin border. It is up to the user agent to determine the actual width.
medium: Specifies a medium width border. It is up to the user agent to determine the actual width.
thick: Specifies a thick border. It is up to the user agent to determine the actual width.
length: Specifies the width of the border using a length value. For example, 10px, 1em, 8pt etc

In addition, all CSS properties also accept the following CSS-wide keyword values as the sole component of their property value:

initial: Represents the value specified as the property's initial value.
inherit: Represents the computed value of the property on the element's parent.
unset: This value acts as either inherit or initial, depending on whether the property is inherited or not. In other words, it sets all properties to their parent value if they are inheritable or to their initial value if not inheritable.

General Information

Initial Value: medium (based on the intial value of the individual properties).
Applies To: All elements.
Inherited?: No
Media: Visual
Animatable: Yes (see example)

Example Code

Official Specifications

CSS Backgrounds and Borders Module Level 3 (W3C Candidate Recommendation 9 September 2014)
CSS Level 2.1 (W3C Recommendation 07 June 2011)
CSS Level 1 (W3C Recommendation 17 Dec 1996)