CSS
Why Do CSS @import Rules Harm Performance?
CSS @import allows developers to load external stylesheets into a CSS file. While this might seem like a convenient way to organize styles, it comes with significant performance drawbacks.
In this blog, we’ll cover:
✅ What @import does
✅ Why @import harms website performance
✅ Best practices to optimize CSS loading
1. What Is CSS @import?
The @import rule allows you to include external stylesheets within a CSS file.
Example:
@import url("styles.css");
or
@import "styles.css";
Instead of linking styles in the HTML <head>, @import enables you to load CSS files from within another CSS file.
2. Why @import Harms Performance
Despite its convenience, @import is bad for performance due to the following reasons:
1. It Increases Page Load Time
When the browser encounters an @import rule, it pauses rendering until the imported CSS file is downloaded and processed.
✅ How It Works:
- The browser loads the main CSS file.
- It finds an
@importstatement and stops rendering. - It fetches the imported file before proceeding.
⛔ Why It’s Bad:
- Causes a delay in rendering the page.
- Slows down the First Contentful Paint (FCP)—an important SEO metric.
2. It Blocks Parallel Downloads
Modern browsers load external CSS files in parallel when linked using <link>.
✅ With <link> in <head>:
<link rel="stylesheet" href="style1.css">
<link rel="stylesheet" href="style2.css">
- Both files download simultaneously.
⛔ With @import:
@import url("style1.css");
@import url("style2.css");
- The browser downloads style1.css first, then downloads style2.css after processing the first file.
- Each import adds a delay.
3. It’s Bad for Render Blocking
CSS blocks page rendering until it fully loads. If styles are imported using @import, the delay increases further because of sequential loading.
✅ Why This Matters:
- Users see a blank page longer.
- Google’s Core Web Vitals penalize slow-loading pages.
4. Older Browser Compatibility Issues
- Internet Explorer 8 and earlier supports only 31 stylesheets when using
@import. - If you exceed this limit, some stylesheets won’t load.
3. What Should You Use Instead?
✅ Use <link> Instead of @import
Instead of @import, use the <link> tag in the HTML <head>.
Example: Using <link> (Best Practice)
<link rel="stylesheet" href="styles.css">
✅ Benefits:
- Styles load faster.
- Multiple stylesheets load in parallel.
- Works with all browsers.
✅ Minify and Combine CSS Files
Instead of loading multiple stylesheets, combine them into one to reduce HTTP requests.
cat style1.css style2.css > main.css
Then, load only one CSS file:
<link rel="stylesheet" href="main.css">
✅ Why?
- Reduces HTTP requests.
- Improves page speed.
4. When Is @import Acceptable?
While @import is not recommended for performance reasons, it may be useful in certain cases:
✅ When using CSS frameworks (e.g., importing Google Fonts).
✅ For modular stylesheets in development (but avoid it in production).
5. Conclusion
Although CSS @import seems convenient, it negatively impacts performance, page load time, and user experience.
❌ Why You Should Avoid @import:
⛔ Blocks page rendering.
⛔ Prevents parallel downloads.
⛔ Increases HTTP requests.
⛔ Causes SEO & performance issues.
✅ Best Alternative:
🚀 Use <link> instead for faster and optimized CSS loading.
By following these best practices, you’ll ensure faster-loading web pages and better SEO rankings.