inset-block-start

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2021.

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

The inset-block-startCSS property defines the logical block start offset of an element, which maps to a physical inset 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.

This inset property has no effect on non-positioned elements.

Try it

writing-mode: horizontal-tb;

writing-mode: vertical-rl;

writing-mode: horizontal-tb; direction: rtl;

writing-mode: vertical-lr;

<section id="default-example"> <div class="example-container" id="example-element"> <div id="abspos"> I am absolutely positioned with inset-block-start: 50px </div> <p> As much mud in the streets as if the waters had but newly retired from the face of the earth, and it would not be wonderful to meet a Megalosaurus, forty feet long or so, waddling like an elephantine lizard up Holborn Hill. </p> </div> </section>

#example-element { border: 0.75em solid; padding: 0.75em; position: relative; width: 100%; min-height: 200px; unicode-bidi: bidi-override; } #abspos { background-color: yellow; color: black; border: 3px solid red; position: absolute; inset-block-start: 50px; inline-size: 140px; }

Syntax

css

/* <length> values */ inset-block-start: 3px; inset-block-start: 2.4em; inset-block-start: anchor(end); inset-block-start: calc(anchor-size(--myAnchor height, 70px) * 2); /* <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: revert; inset-block-start: revert-layer; inset-block-start: unset;

Values

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

Formal definition

Initial value	`auto`
Applies to	positioned elements
Inherited	no
Percentages	logical-height of containing block
Computed value	same as box offsets: `top`, `right`, `bottom`, `left` properties except that directions are logical
Animation type	a length, percentage or calc();

Formal syntax

inset-block-start = 
auto|
<length-percentage>

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

Examples

Setting block start offset

HTML

html

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

CSS

css

div { background-color: yellow; width: 120px; height: 120px; } .exampleText { writing-mode: vertical-lr; position: relative; inset-block-start: 20px; background-color: #c8c800; }

Result

Specifications

Specification
CSS Logical Properties and Values Level 1 # propdef-inset-block-start
CSS Positioned Layout Module Level 3 # propdef-inset-block-start