CSS inset-block-start Property

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span {
  writing-mode: vertical-lr;
  inset-block-start: 50px;


Hello World!


The inset-block-start CSS 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 and bottom, or right and left properties depending on the values defined for writing-mode, direction, and text-orientation.

Default value:auto
JavaScript syntax:

Standard Syntax

inset-block-start: auto|length|%|initial|inherit|revert|revert-layer|unset;

Browser Support


Property Values

The following table describes the values of this property:

Value Description
auto This is default value. The browser calculates the inset block start position.
length Specifies the offset as a length value in px, pt, cm, em, etc. Negative length values are allowed.
%(percentage) Specifies the offset in percentage. The percentage is calculated with respect to the width of the element's containing block. Negative percentage values are allowed.
initial Sets this property to its default value.
inherit If specified, the associated element takes the computed value of its parent element animation-delay property.
revert Reverts the cascaded value of the property from its current value to the value the property
revert-layer Rollback styles to the ones specified in previous cascade layers.
unset Resets a property to its inherited value if the property naturally inherits from its parent, and to its initial value if not.

Default CSS Property Values

selectors {
  inset-block-start: auto;
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