Implementing Critical CSS for Mobile

What is Critical CSS?

Critical CSS refers to the CSS rules that are necessary to render the above-the-fold content of a webpage. By loading only the critical CSS first, you can significantly improve the rendering speed and performance of your mobile applications.

Why Use Critical CSS?

Using Critical CSS has several advantages:

• Improves initial loading time.
• Enhances perceived performance for users.
• Reduces render-blocking requests.

How to Implement Critical CSS

Follow these steps to implement Critical CSS in your mobile applications:

1. Identify Critical CSS:

Use tools like Critical or PurgeCSS to determine which styles are needed for above-the-fold content.

2. Extract Critical CSS:

Once identified, extract the critical CSS into a separate stylesheet. You can do this manually or using build tools.

/* Sample Critical CSS */
body {
    font-family: Arial, sans-serif;
    margin: 0;
}
.header {
    background-color: #007bff;
    color: white;
}

3. Inline Critical CSS:

Inline the critical CSS into the of your HTML document:

<style>
body {
    font-family: Arial, sans-serif;
    margin: 0;
}
.header {
    background-color: #007bff;
    color: white;
}
</style>

4. Load Non-Critical CSS Asynchronously:

Load the rest of your CSS asynchronously:

<link rel="preload" href="styles.css" as="style" onload="this.rel='stylesheet'">

Best Practices

To effectively implement Critical CSS, consider the following best practices:

• Keep critical CSS minimal and specific to the above-the-fold content.
• Test your website performance after implementation using tools like Google PageSpeed Insights.
• Regularly update your critical CSS as your site changes.

FAQ