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

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

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

/* Global keywords */
border-top-width: inherit;
border-top-width: initial;
border-top-width: unset;
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-top-style is none or hidden
Animation type a length
Canonical order the unique non-ambiguous order defined by the formal grammar



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 A thin border
medium A medium border
thick A thick border

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 syntax


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



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


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

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



Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 1 Yes 1 4 3.5 1
Feature Android webview Chrome for Android Edge mobile Firefox for Android IE mobile Opera Android iOS Safari
Basic support 2.3 ? Yes 4 6 11 1

See also

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