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  4. Properties
  5. block-size

block-size CSS property

Baseline
Widely available
*

This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.

* Some parts of this feature may have varying levels of support.

The block-size CSS property defines the size of an element's block along the block axis. If the writing-mode is horizontal, it corresponds to the height; if the writing mode is vertical, it corresponds to the width. A related property is inline-size, which defines the other dimension of the element.

Try it

block-size: 150px;
writing-mode: horizontal-tb;

block-size: 150px;
writing-mode: vertical-rl;

block-size: auto;
writing-mode: horizontal-tb;

block-size: auto;
writing-mode: vertical-lr;

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box where you can change the block-size.
  </div>
</section>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  justify-content: center;
  color: white;
}

Syntax

css
/* <length> values */
block-size: 300px;
block-size: 25em;
block-size: anchor-size(height);
block-size: calc(anchor-size(--my-anchor block) * 0.75);

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

/* Keyword values */
block-size: max-content;
block-size: min-content;
block-size: fit-content;
block-size: fit-content(20em);
block-size: auto;

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

Values

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

Formal definition

Initial valueauto
Applies tosame as width and height
Inheritedno
Percentagesblock-size of containing block
Computed valuesame as width and height
Animation typea length, percentage or calc();

Formal syntax

block-size = 
  auto        |
  <box-size>  

<box-size> = 
  <length-percentage>  |
  stretch              |
  contain              |
  min-content          |
  max-content          |
  fit-content          |
  fit-content( )       |
  calc-size( )         

<length-percentage> = 
  <length>      |
  <percentage>

Examples

Block size with vertical text

HTML

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

CSS

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

Result

Specifications

Specification
CSS Logical Properties and Values Module Level 1
# propdef-block-size

Browser compatibility

See also

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