CSS containment improves performance by isolating elements to limit browser recalculations. 1. The contain property enables developers to specify how isolated an element is from the rest of the page. 2. Values like size, layout, paint, and style offer different levels of containment. 3. strict applies all types of containment, while content excludes size. 4. It's best used on self-contained components like widgets or cards. 5. Performance improvements come from limiting layout, painting, and rendering checks to only the contained element. 6. Avoid overuse as it may cause memory overhead. 7. Browser support varies across containment types, with layout and paint being more widely supported.
CSS containment is a feature that helps improve performance by limiting how much of the page the browser has to re-calculate when something changes. It’s especially useful on complex or large web pages where small updates shouldn’t require the whole page to be re-rendered.
The key idea behind containment is: tell the browser what parts of the page can be treated as independent, so it doesn’t waste time checking unrelated areas when making layout, style, paint, or size calculations.
This is done using the contain
property in CSS.
What does the contain
property do?
The contain
property tells the browser how much a specific element should be isolated from the rest of the page. By doing this, it gives the browser hints about which parts of the page don’t need to be affected when something inside the contained element changes.
You might use it like this:
.widget { contain: strict; }
Or more specifically:
.widget { contain: layout paint size; }
Each value controls a different kind of isolation:
- size – The element’s dimensions are independent of its children.
- layout – Layout inside the element won’t affect anything outside of it.
- paint – Nothing painted inside the element will appear outside it.
- style – Scoped styles — changes inside won’t affect elements outside (still experimental).
- strict – All of the above (size, layout, paint, and style containment).
- content – Same as layout, paint, and style but without size containment.
When should you use containment?
Containment works best when applied to self-contained components — things like widgets, cards, or sidebars that don’t visually or layout-wise depend on other parts of the page.
For example:
- A dynamic widget in a sidebar
- A card component in a grid layout
- A comment section that loads independently
In these cases, wrapping them with contain: content
or contain: layout paint
can help the browser skip unnecessary work during rendering.
Keep in mind:
- Containment only helps if the browser actually uses the hints — not all browsers fully support every option yet.
- Don’t overuse it. Applying
contain
to everything can backfire because it creates extra layers and memory overhead.
How does containment improve performance?
When you update part of a webpage — say, changing some text or toggling a class — the browser usually has to check:
- How that change affects layout (reflow)
- Which parts need to be repainted
- Whether those changes affect other elements
With containment, the browser knows:
- It doesn’t have to look outside the contained box for layout or painting
- It can isolate the rendering process just to that element
So instead of scanning the entire page after a small change, it only needs to re-check that one contained block.
Think of it like sealing off a room before doing messy construction — nothing spills out, and cleanup is easier.
Some practical tips for using contain
Here are a few ways to get started with containment:
- Use
contain: content
on cards or list items that load independently. - Apply
contain: layout paint
to modules that update dynamically (like live feeds or counters). - Avoid applying it to elements that rely heavily on external layout context, such as flex/grid children.
Also keep in mind:
-
contain: strict
is powerful but aggressive — test carefully. - Browser support is decent for layout and paint containment, but size and style are less widely supported.
- Performance gains are more noticeable on large, complex pages.
Basically, CSS containment gives developers a tool to help the browser optimize rendering. It's not always needed, but when used right, it can make your site feel faster and smoother.
The above is the detailed content of What is CSS containment (contain property)?. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

There are three ways to create a CSS loading rotator: 1. Use the basic rotator of borders to achieve simple animation through HTML and CSS; 2. Use a custom rotator of multiple points to achieve the jump effect through different delay times; 3. Add a rotator in the button and switch classes through JavaScript to display the loading status. Each approach emphasizes the importance of design details such as color, size, accessibility and performance optimization to enhance the user experience.

To deal with CSS browser compatibility and prefix issues, you need to understand the differences in browser support and use vendor prefixes reasonably. 1. Understand common problems such as Flexbox and Grid support, position:sticky invalid, and animation performance is different; 2. Check CanIuse confirmation feature support status; 3. Correctly use -webkit-, -moz-, -ms-, -o- and other manufacturer prefixes; 4. It is recommended to use Autoprefixer to automatically add prefixes; 5. Install PostCSS and configure browserslist to specify the target browser; 6. Automatically handle compatibility during construction; 7. Modernizr detection features can be used for old projects; 8. No need to pursue consistency of all browsers,

Themaindifferencesbetweendisplay:inline,block,andinline-blockinHTML/CSSarelayoutbehavior,spaceusage,andstylingcontrol.1.Inlineelementsflowwithtext,don’tstartonnewlines,ignorewidth/height,andonlyapplyhorizontalpadding/margins—idealforinlinetextstyling

Setting the style of links you have visited can improve the user experience, especially in content-intensive websites to help users navigate better. 1. Use CSS's: visited pseudo-class to define the style of the visited link, such as color changes; 2. Note that the browser only allows modification of some attributes due to privacy restrictions; 3. The color selection should be coordinated with the overall style to avoid abruptness; 4. The mobile terminal may not display this effect, and it is recommended to combine it with other visual prompts such as icon auxiliary logos.

Use the clip-path attribute of CSS to crop elements into custom shapes, such as triangles, circular notches, polygons, etc., without relying on pictures or SVGs. Its advantages include: 1. Supports a variety of basic shapes such as circle, ellipse, polygon, etc.; 2. Responsive adjustment and adaptable to mobile terminals; 3. Easy to animation, and can be combined with hover or JavaScript to achieve dynamic effects; 4. It does not affect the layout flow, and only crops the display area. Common usages are such as circular clip-path:circle (50pxatcenter) and triangle clip-path:polygon (50%0%, 100 0%, 0 0%). Notice

To create responsive images using CSS, it can be mainly achieved through the following methods: 1. Use max-width:100% and height:auto to allow the image to adapt to the container width while maintaining the proportion; 2. Use HTML's srcset and sizes attributes to intelligently load the image sources adapted to different screens; 3. Use object-fit and object-position to control image cropping and focus display. Together, these methods ensure that the images are presented clearly and beautifully on different devices.

The choice of CSS units depends on design requirements and responsive requirements. 1.px is used for fixed size, suitable for precise control but lack of elasticity; 2.em is a relative unit, which is easily caused by the influence of the parent element, while rem is more stable based on the root element and is suitable for global scaling; 3.vw/vh is based on the viewport size, suitable for responsive design, but attention should be paid to the performance under extreme screens; 4. When choosing, it should be determined based on whether responsive adjustments, element hierarchy relationships and viewport dependence. Reasonable use can improve layout flexibility and maintenance.

Different browsers have differences in CSS parsing, resulting in inconsistent display effects, mainly including the default style difference, box model calculation method, Flexbox and Grid layout support level, and inconsistent behavior of certain CSS attributes. 1. The default style processing is inconsistent. The solution is to use CSSReset or Normalize.css to unify the initial style; 2. The box model calculation method of the old version of IE is different. It is recommended to use box-sizing:border-box in a unified manner; 3. Flexbox and Grid perform differently in edge cases or in old versions. More tests and use Autoprefixer; 4. Some CSS attribute behaviors are inconsistent. CanIuse must be consulted and downgraded.
