TL;DR
NitroPack’s Combine CSS Files feature merges multiple CSS files into a single one to reduce HTTP requests. This helps your site load faster, improves performance scores, and avoids render-blocking issues—without manual configuration.
CSS (Cascading Style Sheets) defines how your site looks, from fonts and colors to layouts and animations. But while CSS is essential for design, it can slow down page loads if not optimized.
Why?
Each external CSS file is a separate request that the browser must make before rendering the page. When there are many stylesheets, these multiple requests add up, causing delays and blocking visual rendering.
This is known as render-blocking CSS, and it directly affects Core Web Vitals like First Contentful Paint (FCP) and Largest Contentful Paint (LCP).
One way to fix this issue is by combining your CSS files. Read on to learn how you can use it to speed up your WordPress site.
What Does “Combine CSS Files” Mean?
Combining CSS files is a performance optimization technique that merges multiple stylesheet files into a single file.
Instead of loading:
- style.css
- plugin-a.css
- plugin-b.css
Your site loads just one file containing all CSS rules.
This reduces the number of round trips between the browser and the server (HTTP requests), making the page render faster, especially on slower connections.
Test NitroPack yourself
With vs Without Combine CSS Files (Example)
Websites rely on multiple stylesheets from themes, plugins, and custom code. Without combining them, each file adds an extra HTTP request—slowing down the browser’s ability to render content quickly.
By combining CSS files, NitroPack reduces the number of requests dramatically. The result: faster initial render times, improved browser efficiency, and better Core Web Vitals like First Contentful Paint (FCP) and Total Blocking Time (TBT).
| Scenario | Without Combining | With Combining |
| Number of CSS requests | 10+ (theme + plugins) | 1–2 total |
| Initial render time | Slower due to request overhead | Faster rendering |
| Browser efficiency | More HTTP requests | Fewer, leaner downloads |
| Impact on Core Web Vitals | Often high FCP and TBT | Improved FCP and faster interactivity |
Why Is Combining CSS Files Important?
Combining CSS files isn’t just about reducing file counts—it’s about removing friction in the user experience.
Here’s what you gain:
- Faster rendering – Fewer resources to download means the browser can start painting sooner.
- Lower Total Blocking Time (TBT) and Interaction to Next Paint (INP) : Reduced CSS processing leads to faster and smoother interactivity.
- Improved Google PageSpeed scores: Especially on mobile, where bandwidth is limited.
- Better user experience: Visitors see and interact with your content faster.
Bonus: Clears Common PageSpeed Insights Warnings
When CSS is fragmented, PageSpeed Insights might flag issues like:
NitroPack helps resolve these by combining and delivering styles more efficiently—making PSI reports cleaner and your site faster.
Which leads to the question:
How does NitroPack’s Combine CSS feature actually work?
Combine CSS by NitroPack Explained
NitroPack’s Combine CSS Files feature goes beyond basic bundling by using smart logic to optimize performance without compromising design.
It automatically:
- Detects and merges compatible CSS files
- Maintains the correct order of stylesheets to preserve layout and functionality
- Excludes critical or inline styles that should load separately
- Minifies the final combined file for faster delivery
- Avoids combining problematic files by monitoring for compatibility issues
The result:
A single, streamlined CSS file served via our built-in CDN, thus reducing HTTP requests, improving load speed, and keeping your site’s design intact.
But the best part is:
It works out of the box—no coding, plugins, or manual setup required.
NitroPack vs Manual CSS Combining
Manually combining CSS files can be a technical hassle—requiring careful file management, testing for layout breaks, and ongoing updates. One wrong combination can break your design.
NitroPack eliminates that risk by intelligently combining CSS files for you. It automates the process, ensures stable layouts, and delivers everything through its built-in CDN.
| Feature | Manual Combining | NitroPack Combine CSS |
| Setup required | Manual edits or setup tools | Fully automatic |
| Risk of breaking layout | High if the wrong files are combined | Low due to NitroPack’s smart technology |
| CDN delivery | Extra setup required | Included |
| Maintenance | Ongoing | Set it and forget it |
How to Enable Combine CSS Files in NitroPack
Enabling this feature takes just a few clicks:
- Log into your NitroPack dashboard
- Navigate to Cache Settings
- Click on HTML & CSS
- Toggle on Combine CSS
- Save to apply changes
That’s it—NitroPack will take over from there and handle CSS combining dynamically for all eligible stylesheets.
FAQs
Will combining CSS break my site’s design?
No, NitroPack automatically checks compatibility and excludes files that could cause issues.
Do I still need to minify my CSS separately?
No, NitroPack also minifies the combined file for maximum efficiency.
How does this affect mobile performance?
Positively. Fewer requests and smaller payloads make mobile browsing smoother and faster.
