CSS border-block-start Property

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.example1 {
  border-block-start: 5px solid red;

.example2 {
  writing-mode: vertical-lr;
  border-block-start: 5px solid red;

Hello World!


The border-block-start CSS property is a shorthand property for setting the individual logical block-start border property values in a single place in the style sheet.

Default value:medium none currentcolor
JavaScript syntax:
object.style.borderBlockStart="[border-block-start-width border-block-start-style border-block-start-color]|initial|inherit|revert|revert-layer|unset";

Standard Syntax

border-block-start: [border-block-start-width border-block-start-style border-block-start-color]|initial|inherit|revert|revert-layer|unset;

Browser Support


Property Values

The following table describes the values of this property.

Value Description
border-block-start-width Specifies the width of the block-start border of an element.
border-block-start-style Specifies the style of the block-start border of an element.
border-block-start-color Specifies the color of the block-start border of an element.
initial Sets this property to its default value.
inherit If specified, the associated element takes the computed value of its parent element animation-delay property.
revert Reverts the cascaded value of the property from its current value to the value the property
revert-layer Rollback styles to the ones specified in previous cascade layers.
unset Resets a property to its inherited value if the property naturally inherits from its parent, and to its initial value if not.

Default CSS Property Values

selectors {
  border-block-start: medium none currentcolor;
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