Web animations and transitions add life to user interfaces, enhancing interactivity and improving the overall user experience. When used properly, they create smooth, fluid transitions between states—whether it’s a button changing color on hover or a modal sliding into view. However, when misused, they can cause sudden layout shifts, poor performance, and a frustrating user experience. Preventing layout shifts, particularly those that lead to jarring visual jumps or changes in element positioning, is crucial for maintaining a polished, professional website.
In this article, we’ll explore how to master CSS transitions and animations to prevent layout shifts and create a seamless, visually pleasing experience. We’ll break down the common causes of layout shifts, how to use CSS properties effectively, and key best practices for smooth animations. By the end, you’ll have a solid understanding of how to create animations that feel natural, prevent unexpected layout changes, and boost the overall performance of your site.
What Are Layout Shifts?
Layout shifts occur when elements on the page move unexpectedly, often due to the loading or rendering of new content, images, or even misapplied animations. These shifts can be distracting to users, especially on slower connections or devices where delays are more pronounced.
A layout shift might happen when:
- A new image or video loads without predefined dimensions.
- A CSS transition or animation causes elements to move unexpectedly.
- Fonts load late, changing the size or style of text.
- DOM elements are inserted dynamically, pushing surrounding content.
Not only do layout shifts harm user experience, but they also impact Core Web Vitals, specifically the Cumulative Layout Shift (CLS) metric, which measures visual stability. Google considers this an important ranking factor, meaning that poorly managed layout shifts can hurt your SEO performance as well.
Why Do CSS Animations Cause Layout Shifts?
CSS transitions and animations, when misused, can introduce layout shifts by changing the size, position, or spacing of elements in a way that affects other parts of the layout. For instance, animating an element’s width or height without accounting for the space it occupies can push or pull neighboring elements, resulting in an unwanted visual shift.
Here’s an example of a transition causing a layout shift:
.button {
width: 100px;
height: 50px;
transition: width 0.5s ease;
}
.button:hover {
width: 200px; /* The button expands, causing surrounding content to shift */
}
In this case, when the button expands on hover, the rest of the content around it is pushed to accommodate the new size, creating a layout shift that disrupts the page’s visual stability.
Best Practices for Preventing Layout Shifts with CSS Transitions
To prevent layout shifts, it’s important to use CSS properties and techniques that ensure the layout remains stable, even as animations occur. Let’s dive into actionable strategies to master transitions and avoid layout shifts.
1. Animate Transform and Opacity Instead of Width, Height, or Position
When it comes to animations, not all CSS properties are created equal. Animating properties like width
, height
, top
, left
, or margin
often causes layout shifts because they affect the overall flow of the document. On the other hand, properties like transform
and opacity
don’t trigger reflows or repainting of the layout, making them ideal for smooth, shift-free animations.
Here’s why:
Transform allows you to move, scale, or rotate elements without changing their position in the document flow.
Opacity changes the transparency of an element without impacting its surrounding content.
Example of a shift-free animation using transform
:
.button {
width: 100px;
height: 50px;
transform: scale(1);
transition: transform 0.5s ease;
}
.button:hover {
transform: scale(1.2); /* The button scales up without affecting the layout */
}
This method keeps the button in the same place in the document flow while scaling it up, preventing any layout shifts from occurring.
2. Pre-Define Sizes for Images and Media Elements
One of the most common causes of layout shifts is media elements like images, videos, or iframes loading without predefined dimensions. When the browser initially loads the content, it may leave a gap that gets filled later when the media loads, causing a shift.
To prevent this, always define the width
and height
for images and other media elements so that the browser reserves the correct amount of space before the content loads.
Example of pre-defining sizes for an image:
<img src="example.jpg" width="600" height="400" alt="Example Image">
In CSS:
img {
display: block;
width: 100%; /* Ensures responsiveness while preserving aspect ratio */
height: auto;
}
By defining the dimensions, the browser allocates space for the image before it loads, preventing any layout shifts once the image is fully rendered.
3. Use CSS Grid or Flexbox for Stable Layouts
Layout instability can also arise when elements are dynamically added or resized within traditional layout structures like float
or inline-block
. Modern layout techniques like CSS Grid and Flexbox are much more resilient to dynamic content changes, as they are designed to handle flexible layouts while maintaining stability.
For example, using Flexbox allows you to align and distribute space among items in a container without causing shifts, even when content changes.
Example using Flexbox:
.container {
display: flex;
justify-content: space-between;
align-items: center;
}
.item {
width: 150px;
transition: transform 0.3s ease;
}
.item:hover {
transform: scale(1.1); /* No layout shift when scaling items */
}
Here, the justify-content
property evenly distributes space between the items, and animating the transform
property keeps the layout stable while still allowing elements to animate smoothly.
4. Avoid Animating Layout-Affecting Properties (Top, Left, Right, Bottom)
Animating positional properties like top
, left
, right
, and bottom
can lead to layout shifts since they alter the position of the element in the document flow. Instead, use the transform
property to move elements around without affecting the layout.
Example of a smooth animation without layout shifts:
.box {
position: absolute;
top: 50px;
left: 50px;
transition: transform 0.5s ease;
}
.box:hover {
transform: translate(50px, 0); /* Moves the element without layout shifts */
}
By using translate()
in combination with transform
, you move the element to a new position without causing reflows or affecting other elements on the page.
Understanding the Difference Between CSS Transitions and Animations
Before diving further into preventing layout shifts, it’s important to understand the distinction between CSS transitions and CSS animations, as each has different use cases and implications for layout stability.
CSS Transitions: These occur when you change a CSS property, and the browser interpolates the change over a specified duration. Transitions are often used for hover effects or state changes.Example:
.button {
background-color: #3498db;
transition: background-color 0.3s ease;
}
.button:hover {
background-color: #2980b9;
}
CSS Animations: CSS animations allow for more complex, multi-step animations using keyframes. Animations can run automatically when the page loads or when triggered by an event, and they can include multiple properties and states.Example:
@keyframes slide {
from {
transform: translateX(0);
}
to {
transform: translateX(100px);
}
}
.box {
animation: slide 2s ease-in-out;
}
Both transitions and animations can cause layout shifts if not handled properly, particularly when animating layout-affecting properties. The key is to use them thoughtfully, especially when dealing with interactive elements or dynamically loaded content.
Preventing Layout Shifts with Keyframe Animations
Keyframe animations offer more control than transitions, but they can still cause layout shifts if you animate properties that affect the document flow. To avoid this, follow the same principles—animate properties that don’t change the element’s position within the layout.
1. Use Transformations for Movement
If your animation involves moving an element from one place to another, use the transform
property with translate()
instead of animating left
, top
, or similar properties. This keeps the layout stable while allowing the animation to proceed smoothly.
Example of animating movement with keyframes:
@keyframes moveRight {
0% {
transform: translateX(0);
}
100% {
transform: translateX(200px);
}
}
.box {
animation: moveRight 1s ease-in-out;
}
This approach ensures that the movement does not cause reflows or shifts in the surrounding content.
2. Avoid Animating Height and Width
If your animation involves resizing an element, try to avoid directly animating the height
or width
properties. These can cause layout shifts because they change the amount of space the element takes up on the page.
Instead, use scaling with the transform: scale()
property, which enlarges or shrinks the element visually without affecting the surrounding layout.
Example of using scale for resizing:
@keyframes scaleUp {
from {
transform: scale(1);
}
to {
transform: scale(1.5);
}
}
.box {
animation: scaleUp 0.5s ease;
}
This technique creates the illusion of resizing without impacting the layout, ensuring a smoother, more polished user experience.
Optimizing Animations for Performance
In addition to preventing layout shifts, it’s important to optimize your animations for performance, especially on mobile devices or slower connections. Even well-executed animations can feel sluggish or unresponsive if they’re not optimized properly.
1. Use Hardware-Accelerated CSS Properties
Certain CSS properties, like transform
and opacity
, are hardware-accelerated, meaning they’re processed by the GPU instead of the CPU. This results in smoother animations and better overall performance.
Stick to these properties for animations:
transform
opacity
filter
(in some cases)
2. Limit the Number of Simultaneous Animations
While it can be tempting to add multiple animations to various elements, too many simultaneous animations can hurt performance, especially on lower-powered devices. Focus on animating key elements that enhance user experience, and avoid overloading the page with unnecessary animations.
3. Avoid Continuous Animations
Animations that run indefinitely can consume unnecessary resources, especially if they’re not adding value to the user experience. If you use animations for visual effects, such as a rotating loader or pulsating element, make sure they are lightweight and limited in scope.
Advanced Techniques for Preventing Layout Shifts
Now that we’ve covered the basics of preventing layout shifts with CSS transitions and animations, let’s dive deeper into some advanced techniques. These methods are particularly useful when working on complex web applications, where multiple elements need to animate simultaneously or dynamic content is frequently added or removed.
These advanced strategies will help you prevent layout shifts while keeping your site’s performance in check, even in the most demanding scenarios.
1. Reserve Space for Dynamic Content
Layout shifts often happen when dynamic content is loaded into the page, such as when new items are added to a list or a component appears via JavaScript. If the page doesn’t reserve space for this content in advance, other elements get pushed around when the new content arrives.
For example, if you dynamically load a notification banner at the top of a page, the rest of the content will shift downward, creating a jarring experience.
The Solution:
Reserve space for dynamic content by pre-allocating space within the layout or using techniques like placeholders.
Example of reserving space for dynamic content:
<div class="notification-bar"></div>
.notification-bar {
height: 50px; /* Reserve space */
display: none; /* Initially hidden */
}
.notification-bar.active {
display: block; /* When activated, the height remains stable */
}
This approach ensures that when the notification appears, the layout doesn’t shift, and the space for the new content is already accounted for.
Another option is to use CSS’s min-height
or min-width
properties, which ensure that containers can accommodate future content without causing reflows.
.container {
min-height: 400px; /* Reserve space to prevent shifts */
}
2. Use will-change
for Performance Optimization
When you know an element will change (e.g., via a transition or animation), you can use the will-change
property to optimize performance. This property tells the browser to prepare for a change, allowing it to optimize rendering and prevent layout shifts during the animation.
However, be cautious with will-change
because overusing it can negatively impact performance by consuming more resources than necessary.
Example of using will-change
:
.button {
will-change: transform; /* Hint to the browser that transform will change */
transition: transform 0.3s ease;
}
.button:hover {
transform: scale(1.2);
}
By specifying will-change: transform
, the browser is better prepared to handle the upcoming animation, ensuring smooth transitions without layout shifts.
3. Optimize Font Loading to Prevent Shifts
Font loading is another common cause of layout shifts, particularly when a web font is loaded after the initial page render. When the browser renders fallback fonts and then switches to the correct font, the change in font size or style can cause layout shifts.
The Solution:
Use the Font Loading API or CSS properties like font-display
to control how fonts are rendered, reducing layout shifts caused by font changes.
Example using font-display
:
@font-face {
font-family: 'MyCustomFont';
src: url('my-custom-font.woff2') format('woff2');
font-display: swap; /* Ensures fallback font is displayed until the custom font loads */
}
The swap
value allows the browser to use a fallback font until the custom font has fully loaded, preventing layout shifts caused by late font rendering. This ensures that the content remains visible and stable while waiting for the correct font.
4. Lazy-Load Images with Placeholder Dimensions
Lazy-loading images can improve performance by deferring the loading of images that aren’t immediately visible. However, if the image dimensions aren’t defined upfront, lazy-loading can cause layout shifts as the page adjusts to accommodate the loaded images.
The Solution:
Define the width and height of images upfront to ensure the layout remains stable, even before the image is loaded. You can also use low-resolution placeholder images (or even CSS-based placeholders) to visually fill the space until the full image loads.
Example of lazy-loading with predefined dimensions:
<img src="large-image.jpg" alt="Example Image" width="800" height="600" loading="lazy">
This approach ensures the image doesn’t cause a layout shift when it’s loaded. By predefining the dimensions, the browser knows how much space to allocate in advance.
You can also use a CSS-based placeholder, which provides a smoother user experience:
img {
width: 100%;
height: auto;
background-color: #f0f0f0; /* Placeholder color */
}
This ensures that even while the image is loading, the placeholder occupies the intended space and prevents any shifting.
5. Consider Flexbox’s align-content
and justify-content
When using Flexbox to align elements, improper use of properties like align-content
and justify-content
can sometimes cause layout shifts when elements are resized or repositioned. Flexbox is great for creating responsive layouts, but it’s important to ensure that these properties are set up in a way that maintains layout stability.
The Solution:
Make sure that Flexbox properties are set in a way that prevents sudden reflows or layout changes when elements are resized or dynamically added.
Example of using Flexbox for stable layouts:
.flex-container {
display: flex;
justify-content: space-between;
align-items: center;
}
.flex-item {
width: 200px;
transition: transform 0.3s ease;
}
.flex-item:hover {
transform: scale(1.1); /* No layout shift while animating */
}
In this case, using justify-content: space-between
ensures that the layout remains evenly distributed, even when individual items change size or position. Additionally, by animating with transform
, no layout shifts occur during the hover animation.
Measuring Layout Shifts with Core Web Vitals
Preventing layout shifts isn’t just about visual polish; it directly impacts your website’s performance metrics, particularly Cumulative Layout Shift (CLS). CLS is one of the Core Web Vitals, which are essential metrics for measuring the user experience and performance of a webpage.
What Is CLS?
CLS measures the sum total of all layout shifts that occur while a page is being used. A good CLS score indicates that the page remains visually stable, with minimal unexpected movements. A low CLS score (below 0.1) is considered ideal for providing a smooth, stable experience.
Tools for Measuring and Preventing Layout Shifts
To ensure your site meets the Core Web Vitals standards and provides a stable user experience, it’s essential to track and measure CLS using tools like:
Google Lighthouse: Part of Chrome’s DevTools, Lighthouse audits your site’s performance, including layout shifts.
PageSpeed Insights: Google’s PageSpeed Insights tool analyzes a site’s CLS score and provides recommendations for improvement.
Web Vitals Extension: This Chrome extension provides real-time metrics for Core Web Vitals, including CLS, directly within the browser.
By using these tools, you can pinpoint where layout shifts are happening on your site and adjust your animations and transitions accordingly to improve user experience and SEO performance.
Conclusion: Achieving Smooth Animations Without Layout Shifts
Mastering CSS transitions and animations is key to creating a seamless and engaging user experience. However, without careful planning, animations can lead to layout shifts, which disrupt visual stability and harm both user experience and SEO performance. By following the best practices outlined in this article—focusing on animating transform and opacity, predefining media sizes, and using modern layout techniques like Flexbox and Grid—you can ensure that your animations are smooth, performant, and free of layout shifts.
At PixelFree Studio, we believe that great design is about more than just aesthetics. It’s about creating a fluid, intuitive experience for your users that performs well on every device and in every browser. By taking control of your CSS animations and preventing layout shifts, you’ll deliver a polished, professional web experience that keeps users engaged and boosts your site’s performance across the board.
Read Next: