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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 top, right, bottom, 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 value	`auto`
Applies to	positioned elements
Inherited	no
Percentages	logical-height of containing block
Media	visual
Computed value	same as box offsets: `top`, `right`, `bottom`, `left` properties except that directions are logical
Animation type	a length, percentage or calc();
Canonical order	the 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 compatibilityUpdate compatibility data on GitHub

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	No	?	63 63 41 — 63 Uses the non-standard name: `offset-block-start` 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	No	No

	Mobile
	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet
Basic support	No	?	?	63 63 41 — 63 Uses the non-standard name: `offset-block-start` 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	No	No