Web/CSS/contain

The contain CSS property allows an author to indicate that an element and its contents are, as much as possible, independent of the rest of the document tree. This allows the browser to recalculate layout, style, paint, size, or any combination of them for a limited area of the DOM and not the entire page, leading to obvious performance benefits.

This property is useful on pages that contain a lot of widgets that are all independent, as it can be used to prevent each widget's internals from having side effects outside of the widget's bounding-box.

Note: If applied (with value: paint, strict or content), this property creates:

A new containing block (for the descendants whose position property is absolute or fixed).
A new stacking context.
A new block formatting context.

Syntax

/* Keyword values */
contain: none;
contain: strict;
contain: content;
contain: size;
contain: layout;
contain: style;
contain: paint;

/* Multiple keywords */
contain: size paint;
contain: size layout paint;

/* Global values */
contain: inherit;
contain: initial;
contain: unset;

The contain property is specified as either one of the following:

Using a single none, strict, or content keyword.
Using one or more of the size, layout, style, and paint keywords in any order.

Values

none: Indicates the element renders as normal, with no containment applied.
strict: Indicates that all containment rules except style are applied to the element. This is equivalent to contain: size layout paint.
content: Indicates that all containment rules except size and style are applied to the element. This is equivalent to contain: layout paint.
size: Indicates that the element can be sized without the need to examine its descendants' sizes.
layout: Indicates that nothing outside the element may affect its internal layout and vice versa.
style: Indicates that, for properties that can have effects on more than just an element and its descendants, those effects don't escape the containing element. Note that this value is marked "at-risk" in the spec and may not be supported everywhere.
paint: Indicates that descendants of the element don't display outside its bounds. If the containing box is offscreen, the browser does not need to paint its contained elements — these must also be offscreen as they are contained completely by that box. And if a descendant overflows the containing element's bounds, then that descendant will be clipped to the containing element's border-box.

Formal definition

Initial value	`none`
Applies to	all elements
Inherited	no
Computed value	as specified
Animation type	discrete

Formal syntax

none | strict | content | [ size || layout || style || paint ]

Examples

Simple layout

The markup below consists of a number of articles, each with content:

<h1>My blog</h1>
<article>
  <h2>Heading of a nice article</h2>
  <p>Content here.</p>
</article>
<article>
  <h2>Another heading of another article</h2>
  <img src="graphic.jpg" alt="photo">
  <p>More content here.</p>
</article>

Each <article> and <img> is given a border, and the images are floated:

img {
  float: left;
  border: 3px solid black;
}

article {
  border: 1px solid black;
}

You can immediately see an issue — no effort is made to clear the floating beyond the bottom of the article.

Float interference

If we were to insert another image at the bottom of the first article, a large portion of the DOM tree may be re-laid out or repainted, and this would interfere further with the layout of the second article:

<h1>My blog</h1>
<article>
  <h2>Heading of a nice article</h2>
  <p>Content here.</p>
  <img src="i-just-showed-up.jpg" alt="social">
</article>
<article>
  <h2>Another heading of another article</h2>
  <img src="graphic.jpg" alt="photo">
  <p>More content here.</p>
</article>

img {
  float: left;
  border: 3px solid black;
}

article {
  border: 1px solid black;
}

As you can see, because of the way floats work, the first image ends up inside the area of the second article:

Fixing with contain

If we give each article the contain property with a value of content, when new elements are inserted the browser understands it only needs to recalculate the containing element's subtree, and not anything outside it:

<h1>My blog</h1>
<article>
  <h2>Heading of a nice article</h2>
  <p>Content here.</p>
  <img src="i-just-showed-up.jpg" alt="social">
</article>
<article>
  <h2>Another heading of another article</h2>
  <img src="graphic.jpg" alt="photo">
  <p>More content here.</p>
</article>

img {
  float: left;
  border: 3px solid black;
}

article {
  border: 1px solid black;
  contain: content;
}

This also means that the first image no longer floats down to the second article, and instead stays inside it's containing element's bounds:

Specifications

Specification	Status	Comment
CSS Containment Module Level 2The definition of 'contain' in that specification.	Working Draft	Added `style` keyword

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`contain`	Chrome Full support 52	Edge Full support 79	Firefox Full support 69 Notes' Full support 69 Notes' Notes' Firefox does not support the `style` value. Full support 41 Disabled' Disabled' From version 41: this feature is behind the `layout.css.contain.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera Full support 40	Safari No support No	WebView Android Full support 52	Chrome Android Full support 52	Firefox Android Full support 41 Notes' Disabled' Full support 41 Notes' Disabled' Notes' Firefox does not support the `style` value. Disabled' From version 41: this feature is behind the `layout.css.contain.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	Opera Android Full support 41	Safari iOS No support No	Samsung Internet Android Full support 6.0

Legend

Full support: Full support
No support: No support
See implementation notes.': See implementation notes.
User must explicitly enable this feature.': User must explicitly enable this feature.