Maximizing Performance with CSS Containment

CSS containment is a powerful tool that can help developers optimize the performance of their web pages by isolating certain elements and their styles. This technique allows browsers to better prioritize rendering tasks, ultimately leading to a faster, more efficient browsing experience. In this blog post, we'll cover the basics of CSS containment, explore some key use cases, and learn how to implement it in your projects. Along the way, we'll provide detailed code examples and explanations to help you get started. Let's dive in!

Understanding CSS Containment

CSS containment is a feature that provides a way for developers to specify that an element's layout, style, paint, and size should be contained and not affect other elements in the DOM (Document Object Model). By isolating specific elements, browsers can perform optimizations that improve rendering performance, such as avoiding unnecessary layout calculations and minimizing paint operations.

To implement CSS containment, you'll need to use the contain property. This property accepts several values that define the type of containment you want to apply to an element:

• size: The element's size is isolated, and any changes to its size will not affect the layout of other elements.
• layout: The element's layout is isolated, meaning that its position and size will not influence the position or size of other elements.
• style: The element's style is isolated, so any style changes will not cause recalculations of styles for other elements.
• paint: The element's paint is isolated, preventing it from drawing outside of its bounds or causing other elements to redraw.
• strict: This value is a shorthand for applying all the containment types (size, layout, style, and paint) to the element.

Now that we have a basic understanding of CSS containment, let's explore some practical use cases and learn how to implement it in your projects.

Use Case 1: Preventing Layout Shifts

One common issue that developers face is layout shifts, which occur when the position or size of elements on a page changes unexpectedly. This can cause a frustrating user experience, as content may move or reflow as the page loads. To address this issue, you can use CSS containment to isolate the layout of specific elements, ensuring that they don't affect other elements on the page.

Consider the following example:

<div class="container">
  <div class="box"></div>
  <div class="content">...</div>
</div>

.container {
  display: flex;
}

.box {
  flex-shrink: 0;
  width: 200px;
  height: 200px;
  background-color: red;
  margin-right: 16px;
}

.content {
  /* ... */
}

In this example, if the size of the .box element changes, it may cause the .content element to reflow. To prevent this, we can apply layout containment to the .box element:

.box {
  contain: layout;
  flex-shrink: 0;
  width: 200px;
  height: 200px;
  background-color: red;
  margin-right: 16px;
}

By doing this, we ensure that any changes to the .box element's size will not affect the layout of the .content element.

Use Case 2: Improving Scrolling Performance

When a page has complex elements or animations, scrolling performance can be negatively impacted. One way to improve scrolling performance is by isolating the paint of elements that are likely to cause repaints, such as those with animations or transitions.

For example, consider the following animated element:

<div class="animated-element">...</div>

.animated-element {
  width:100px;
  height: 100px;
  background-color: blue;
  animation: move 3s linear infinite;
}

@keyframes move {
  0% {
    transform: translateY(0);
  }
  100% {
    transform: translateY(100%);
  }
}

In this example, the .animated-element continuously moves vertically, which may cause performance issues as the browser must repaint it frequently. To improve scrolling performance, we can apply paint containment to the .animated-element:

.animated-element {
  contain: paint;
  width: 100px;
  height: 100px;
  background-color: blue;
  animation: move 3s linear infinite;
}

By applying paint containment, we ensure that the .animated-element does not cause other elements to repaint as it moves, leading to better scrolling performance.

Use Case 3: Isolating Third-Party Widgets

When using third-party widgets, such as social media buttons or ads, it's essential to isolate their styles to prevent them from affecting your page's layout and performance. CSS containment can help you achieve this by isolating the layout, paint, and style of the widget.

Consider the following example of a third-party widget:

<div class="widget-container">
  <iframe src="https://example-widget.com" class="widget"></iframe>
</div>

.widget-container {
  position: relative;
}

.widget {
  border: none;
  width: 100%;
  height: 300px;
}

To isolate the widget, you can apply the strict containment value to the .widget-container:

.widget-container {
  contain: strict;
  position: relative;
}

By doing this, we ensure that the widget's layout, paint, and style are isolated, preventing any potential issues with the rest of the page.

Frequently Asked Questions (FAQ)

Q: Can I apply multiple containment values to a single element?

A: Yes, you can apply multiple containment values to a single element by specifying them as a space-separated list. For example, to apply layout and paint containment, you would use contain: layout paint;.

Q: What are the browser compatibility considerations for CSS containment?

A: As of September 2021, CSS containment is supported in the latest versions of Chrome, Firefox, and Safari. Internet Explorer and early versions of Microsoft Edge do not support CSS containment. To ensure compatibility, you can use feature detection with the @supports rule or check the compatibility on Can I use.

Q: Does CSS containment impact the accessibility of my page?

A: No, CSS containment should not negatively impact the accessibility of your page. The contain property only affects the layout, paint, and style calculations of elements, not their functionality or accessibility-related properties.

Q: Are there any performance drawbacks to using CSS containment?

A: While CSS containment can greatly improve rendering performance in many cases, it's essential to use it judiciously. Overusing containment can lead to unnecessary overhead and, in some cases, even reduced performance. Apply containment only to the elements that are likely to benefit from it, such as those with complex styles, animations, or third-party content.