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block-size

This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The block-size CSS property defines the horizontal or vertical size of an element's block, depending on its writing mode. It corresponds to either the width or the height property, depending on the value of writing-mode.

Syntax

/* <length> values */
block-size: 300px;
block-size: 25em;

/* <percentage> values */
block-size: 75%;

/* Keyword values */
block-size: 25em border-box;
block-size: 75% content-box;
block-size: max-content;
block-size: min-content;
block-size: available;
block-size: fit-content;
block-size: auto;

/* Global values */
block-size: inherit;
block-size: initial;
block-size: unset;

If the writing mode is vertically oriented, the value of block-size relates to the width of the element; otherwise, it relates to the height of the element. A related property is inline-size, which defines the other dimension of the element.

Initial value	`auto`
Applies to	same as `width` and `height`
Inherited	no
Percentages	block-size of containing block
Media	visual
Computed value	same as `width` and `height`
Animation type	discrete
Canonical order	the unique non-ambiguous order defined by the formal grammar

Syntax

Values

The block-size property takes the same values as the width and height properties.

Formal syntax

<'width'>

Example

HTML

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

CSS

.exampleText {
  writing-mode: vertical-rl;
  background-color: yellow;
  block-size: 200px;
}

Specification

Specification	Status	Comment
CSS Logical Properties and Values Level 1 The definition of 'block-size' in that specification.	Editor's Draft	Initial definition

Browser compatibilityUpdate compatibility data on GitHub

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	57	No	41 41 38 — 51 Disabled Disabled From version 38 until version 51 (exclusive): this feature is behind the `layout.css.vertical-text.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No	44	No

	Mobile
	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet
Basic support	57	57	No	41 41 38 — 51 Disabled Disabled From version 38 until version 51 (exclusive): this feature is behind the `layout.css.vertical-text.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	44	No	No

block-size

Syntax

Syntax

Values

Formal syntax

Example

HTML

CSS

Specification

Browser compatibilityUpdate compatibility data on GitHub

See also