border-block-start - CSS

Try it

border-block-start: solid; writing-mode: horizontal-tb;

border-block-start: dashed red; writing-mode: vertical-rl;

border-block-start: 1rem solid; writing-mode: horizontal-tb;

border-block-start: thick double #32a1ce; writing-mode: vertical-lr;

<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: #eeeeee; color: darkmagenta; padding: 0.75em; width: 80%; height: 100px; unicode-bidi: bidi-override; }

Constituent properties

This property is a shorthand for the following CSS properties:

Syntax

css

border-block-start: 1px; border-block-start: 2px dotted; border-block-start: medium dashed blue; /* Global values */ border-block-start: inherit; border-block-start: initial; border-block-start: revert; border-block-start: revert-layer; border-block-start: unset;

border-block-start can be used to set the values for one or more of border-block-start-width, border-block-start-style, and border-block-start-color. The physical border to which it maps depends on the element's writing mode, directionality, and text orientation. It corresponds to the border-top, border-right, border-bottom, or border-left property depending on the values defined for writing-mode, direction, and text-orientation.

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

Values

The border-block-start is specified with one or more of the following, in any order:

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

Formal definition

Initial value	as each of the properties of the shorthand: `border-width`: as each of the properties of the shorthand: `border-top-width`: `medium` `border-right-width`: `medium` `border-bottom-width`: `medium` `border-left-width`: `medium` `border-style`: as each of the properties of the shorthand: `border-top-style`: `none` `border-right-style`: `none` `border-bottom-style`: `none` `border-left-style`: `none` `color`: `canvastext`
Applies to	all elements
Inherited	no
Computed value	as each of the properties of the shorthand: `border-width`: as each of the properties of the shorthand: `border-bottom-width`: the absolute length or `0` if `border-bottom-style` is `none` or `hidden` `border-left-width`: the absolute length or `0` if `border-left-style` is `none` or `hidden` `border-right-width`: the absolute length or `0` if `border-right-style` is `none` or `hidden` `border-top-width`: the absolute length or `0` if `border-top-style` is `none` or `hidden` `border-style`: as each of the properties of the shorthand: `border-bottom-style`: as specified `border-left-style`: as specified `border-right-style`: as specified `border-top-style`: as specified `border-block-start-color`: computed color
Animation type	as each of the properties of the shorthand: `border-block-start-color`: by computed value type `border-block-start-style`: discrete `border-block-start-width`: by computed value type

Formal syntax

border-block-start = 
 <line-width> ||
 <line-style> ||
 <color> 

<line-width> = 
 <length [0,∞]> |
 thin |
 medium |
 thick 

<line-style> = 
 none |
 hidden |
 dotted |
 dashed |
 solid |
 double |
 groove |
 ridge |
 inset |
 outset

Examples

Border with vertical text

HTML

html

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

CSS

css

div { background-color: yellow; width: 120px; height: 120px; } .exampleText { writing-mode: vertical-rl; border-block-start: 5px dashed blue; }

Specifications

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

Browser compatibility

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This page was last modified on ⁨Dec 5, 2025⁩ by MDN contributors.

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