inset-block-start

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

The inset-block-start CSS property defines the logical block start offset of an element, which maps to a physical offset depending on the element's writing mode, directionality, and text orientation. It corresponds to the toprightbottom, or left property depending on the values defined for writing-mode, direction, and text-orientation.

Note: Prior to Firefox 63 this property was implemented as offset-block-start. Firefox 63 updated the name of this property to match a change to the specification.

/* <length> values */
inset-block-start: 3px;
inset-block-start: 2.4em;

/* <percentage>s of the width or height of the containing block */
inset-block-start: 10%;

/* Keyword value */
inset-block-start: auto;

/* Global values */
inset-block-start: inherit;
inset-block-start: initial;
inset-block-start: unset;

It relates to inset-block-end, inset-inline-start, and inset-inline-end, which define the other offsets of the element.

Initial valueauto
Applies topositioned elements
Inheritedno
Percentageslogical-height of containing block
Mediavisual
Computed valuesame as box offsets: top, right, bottom, left properties except that directions are logical
Animation typea length, percentage or calc();
Canonical orderthe unique non-ambiguous order defined by the formal grammar

Syntax

Values

The inset-block-start property takes the same values as the left property.

Formal syntax

<'left'>

Example

HTML Content

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

CSS Content

div {
  background-color: yellow;
  width: 120px;
  height: 120px;
}

.exampleText {
  writing-mode: vertical-lr;
  position: relative;
  inset-block-start: 20px;
  background-color: #c8c800;
}

Specification

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

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic support
Experimental
Chrome No support NoEdge ? Firefox Full support 63
Full support 63
No support 41 — 63
Alternate Name
Alternate Name Uses the non-standard name: offset-block-start
No support 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.
IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android ? Edge Mobile ? Firefox Android Full support 63
Full support 63
No support 41 — 63
Alternate Name
Alternate Name Uses the non-standard name: offset-block-start
No support 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.
Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support No

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
User must explicitly enable this feature.
User must explicitly enable this feature.
Uses a non-standard name.
Uses a non-standard name.

See also

Document Tags and Contributors

Last updated by: chrisdavidmills,