CSS border-block-start-width Property

CSS border-block-start-width

The border-block-start-width property in CSS specifies the width of the block-start border of an element. The block-start side depends on the element’s writing mode, directionality, and text orientation. This property allows you to control the width of the block-start border independently.

Syntax of border-block-start-width

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border-block-start-width: medium | thin | thick | length | initial | inherit;

Values

Value	Description
`medium`	Specifies a medium border width. This is the default value.
`thin`	Specifies a thin border width.
`thick`	Specifies a thick border width.
`length`	Specifies the width of the border in a specific length unit (e.g., `2px`, `1em`).
`initial`	Sets the property to its default value (`medium`).
`inherit`	Inherits the value from its parent element.

Default Value

medium

Examples for border-block-start-width

Using the CSS border-block-start-width Property

The following examples demonstrate how to use the border-block-start-width property to set the width of the block-start border.

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/* Set the block-start border width to medium */
.element {
  border-block-start-width: medium;
}

/* Set the block-start border width to thin */
.element {
  border-block-start-width: thin;
}

/* Set the block-start border width to 5px */
.element {
  border-block-start-width: 5px;
}

/* Inherit the block-start border width from the parent */
.element {
  border-block-start-width: inherit;
}

Example for Thick Block-Start Border

Below is an example demonstrating how to use border-block-start-width: thick to apply a thick border to the block-start side:

index.html

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<!DOCTYPE html>
<html lang="en">
<head>
<style>
  .box {
    width: 300px;
    padding: 10px;
    border-block-start-width: thick;
    border-block-start-style: solid;
  }
</style>
</head>
<body>

<h2 class="box">Lorem Ipsum</h2>

</body>
</html>

Example for Block-Start Border Width in Pixels

border-block-start-width: 20px;

index.html

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<!DOCTYPE html>
<html lang="en">
<head>
<style>
  .box {
    width: 300px;
    padding: 10px;
    border-block-start-width: 20px;
    border-block-start-style: solid;
  }
</style>
</head>
<body>

<h2 class="box">Lorem Ipsum</h2>

</body>
</html>

Browser Support

The border-block-start-width property is supported in modern browsers. Below is a compatibility table:

Browser	Version
Chrome	69.0
Edge	79.0
Firefox	41.0
Safari	12.1
Opera	56.0

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CSS border-block-start-width Property