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border-block-start-width

The border-block-start-width CSS property defines the width of the logical block-start border 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, border-right-width, border-bottom-width, or border-left-width property depending on the values defined for writing-mode, direction, and text-orientation.

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Syntax

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

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

Related properties are border-block-end-width, border-inline-start-width, and border-inline-end-width, which define the other border widths of the element.

Values

<'border-width'>: The width of the border. See border-width.

Formal definition

Initial value	`medium`
Applies to	all elements
Inherited	no
Percentages	logical-width of containing block
Computed value	absolute length; `0` if the border style is `none` or `hidden`
Animation type	a length

Formal syntax

border-block-start-width = 
  <'border-top-width'>

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-start-width: 5px;
}

Results

Specifications

Specification
CSS Logical Properties and Values Level 1 # border-width

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`border-block-start-width`	69	79	41	No	56	12.1	69	69	41	48	12.2	10.0