The contain property in CSS improves performance by isolating an element’s layout, paint, or style. 1. It tells the browser that changes inside the element won’t affect content outside it. 2. Common values include layout, paint, style, and strict, which control different aspects of rendering containment. 3. Use it for self-contained components like cards or lists to optimize rendering. 4. Be cautious with size and paint as they may cause layout issues or clipping. 5. Browser support is broad but should be tested in older environments. Applying contain correctly can boost performance without altering visual appearance.
The contain
property in CSS is a way to tell the browser how much a specific element is independent from the rest of the page. This can help with performance by limiting how much the browser needs to recalculate layout, style, paint, or size when changes happen inside that element.

Here’s what you really need to know about it:
What Does contain
Actually Do?
At its core, contain
lets the browser optimize rendering by isolating an element. When you apply contain
, you're basically saying:

"This element doesn’t affect much outside of itself, so feel free to optimize around it."
Depending on the value used (like layout
, paint
, style
, or combinations), the browser knows which parts of rendering it can safely contain within that element.

Common Values and When to Use Them
There are several values for contain
. Here are the most useful ones:
-
layout
– The internal layout of the element doesn’t affect anything outside of it. -
paint
– Nothing painted inside this element will appear outside its bounds. -
style
– The element's styles won't affect elements outside of it. -
size
– The element’s dimensions don’t depend on its children. -
strict
– All of the above: full containment. -
content
– Likestrict
, but excludessize
containment.
For example, if you have a card component that doesn’t influence the layout of other items on the page, using contain: layout paint style
could help speed things up without side effects.
Practical Use Cases
You might want to use contain
in these kinds of situations:
- In large lists or grids where each item is self-contained
- In reusable components like cards, modals, or widgets
- To prevent style leakage between different sections of a page
- When optimizing performance on complex pages
Let’s say you have a list of blog posts. Each post has its own heading, image, and text. Applying contain: content
to each .post
container tells the browser that they’re isolated and can be handled separately — potentially improving rendering efficiency.
A Few Things to Watch Out For
Using contain
isn’t always straightforward. Here are some gotchas:
- If you set
contain: size
, make sure the element has a defined height and width — otherwise, it might collapse. - Some positioning tricks (like absolutely positioned elements extending beyond their parent) might get clipped if
contain: paint
is used. - Browser support is pretty good, but test carefully if you're targeting older environments.
If you're not seeing the effect you expect, double-check your HTML structure and the exact value of contain
you’ve applied.
That’s basically it. contain
isn’t something you’ll use every day, but when you do, it can quietly improve performance without changing how your site looks.
The above is the detailed content of What is the `contain` property in CSS?. For more information, please follow other related articles on the PHP Chinese website!

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