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css property

`border-block-width` CSS property

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The border-block-width CSS property defines the width of the logical block borders of an element, which maps to a physical border width depending on the element’s writing mode, directionality, and text orientation. It corresponds to the border-top-width and border-bottom-width, or border-left-width, and border-right-width property depending on the values defined for writing-mode, direction, and text-orientation.

The border width in the other dimension can be set with border-inline-width, which sets border-inline-start-width, and border-inline-end-width.

Interactive exampleOpen the canonical MDN source to run this embedded demo.
border-block-width: thick;
writing-mode: horizontal-tb;

border-block-width: thick;
writing-mode: vertical-rl;

border-block-width: 4px;
writing-mode: horizontal-tb;
direction: rtl;

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box with a border around it.
  </div>
</section>

#example-element {
  background-color: palegreen;
  color: black;
  border: 0 solid crimson;
  padding: 0.75em;
  width: 80%;
  height: 100px;
  unicode-bidi: bidi-override;
}

Syntax

/* <'line-width'> values */
border-block-width: 5px;
border-block-width: thick;

/* Global values */
border-block-width: inherit;
border-block-width: initial;
border-block-width: revert;
border-block-width: revert-layer;
border-block-width: unset;

Values

  • &lt;line-width&gt;
    • : Defines the width of the border, either as an explicit non-negative &lt;length&gt; or the keywords: thin, medium, or thick. The default is medium.

Formal definition

Formal syntax

Examples

Border width with vertical text

HTML

<div>
  <p class="exampleText">Example text</p>
</div>

CSS

div {
  background-color: yellow;
  width: 120px;
  height: 120px;
}

.exampleText {
  writing-mode: vertical-lr;
  border: 1px solid blue;
  border-block-width: 5px;
}

Results

Interactive exampleOpen the canonical MDN source to run this embedded demo.

Specifications

SpecificationsStandards references are available on the canonical MDN page.

Browser compatibility

Browser compatibilityCompatibility data is available on the canonical MDN page.

See also