The max-width CSS descriptor specifies the maximum width of the viewport of a document defined via @viewport.

By default, max-width is set as close as possible to the initial viewport width within the minimum and maximum width constraints.

Related at-rule@viewport
Initial valueauto
Percentagesrefer to the width of the initial viewport
Mediavisual, continuous
Computed valueif specified as a length, the corresponding absolute length; if specified as a percentage, the specified value; otherwise, auto
Canonical orderthe unique non-ambiguous order defined by the formal grammar


@viewport {
    max-width: 320px;


The used value is calculated from the other CSS descriptors' values.
A non-negative absolute or relative length.
A percentage value relative to the width or height of the initial viewport at zoom factor 1.0, for horizontal and vertical lengths respectively. Must be non-negative.

Formal syntax

auto | <length> | <percentage>


Specification Status Comment
CSS Device Adaptation
The definition of '"min-width" descriptor' in that specification.
Working Draft Initial definition

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 29 (behind a flag) Not supported 10 -ms 11.10
Removed in 15
Reintroduced behind a flag in 16
Not supported
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support
Not supported 10-ms 11.10
Removed in 15
Reintroduced behind a flag in 16
Not supported


Document Tags and Contributors

 Contributors to this page: mrenty, tuttza
 Last updated by: mrenty,