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

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


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

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

border-top-width: inherit;


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

Formal syntax


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


element { 
    border-top-width: thin;
    border-top-style: solid;
    border-top-color: #000;
	border-top: thick solid red;
	border-top: medium solid orange;
	border-top: thin solid green;

Live Sample

Element 1
Element 2
Element 3


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

Browser compatibility

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

See also

Document Tags and Contributors

 Last updated by: Sebastianz,