CSS plays a very big role in creating any website and giving it its overall look and feel. It is often called the backbone of a website — without CSS, you simply cannot build a proper website. You can even say that it’s impossible to imagine a website without CSS.
Every element on a webpage — where it should be placed, how it should appear, how much margin or padding it should have — all of this is controlled by CSS. In short, we cannot design a website without CSS.
Once the design is complete, the next important step is to check the loading speed of the website. Website speed means how much time it takes for the site to load when we open it on a server.
To improve website speed, we need to follow a few steps so that the website loads properly and opens quickly whenever someone visits it.
Before jumping into tips, it’s important to understand how CSS affects key metrics:
1. Why CSS Impacts Core Web Vitals
- Largest Contentful Paint (LCP): Large CSS files or render-blocking styles delay the time it takes for the biggest visible element to appear.
- Cumulative Layout Shift (CLS): Poorly managed CSS (like missing dimensions or late-loading fonts) can cause layout jumps.
- First Input Delay (FID): Although mainly JavaScript-related, bloated CSS can still delay first paint, indirectly affecting perceived interactivity.
Optimizing CSS reduces file size, removes blocking, and ensures content appears and stabilizes faster.
2. Inline Critical CSS
Critical CSS refers to the styles needed for the above-the-fold content. By inlining critical CSS in the <head>, you ensure that the first visible portion of the page loads instantly without waiting for the full stylesheet.
How to implement:
- Identify critical styles using tools like Lighthouse, Chrome DevTools, or manual extraction.
- Inline only the minimal styles required for the first viewport.
- Load the rest of the CSS asynchronously.
<style>
/* Critical styles here (header, hero section, navigation) */
body { margin:0; font-family: system-ui; }
.header { display:flex; justify-content:space-between; }
</style>
<link rel="preload" href="styles.css" as="style" onload="this.rel='stylesheet'">3. Minify and Compress CSS
Large CSS files directly slow down LCP. Minifying removes unnecessary whitespace and comments, while compression (like Gzip or Brotli) reduces file size further.
Steps:
- Use build tools like Vite, Webpack, or Gulp for automated minification.
- Enable Gzip/Brotli compression on the server.
- Combine small CSS files to reduce HTTP requests.
4. Avoid Render-Blocking CSS
External CSS files loaded in the <head> block rendering until they’re downloaded. To fix this:
- Use media attributes (e.g.,
media="print") for non-critical styles. - Preload key CSS files with
<link rel="preload">. - Load non-critical CSS asynchronously using
onload.
5. Write Shorter CSS
Whenever you have CSS styles that are the same for multiple elements, like if you use h1 and h2 both with 40px font size, you don’t need to write separate CSS for each. Instead, you can write the CSS together using a comma.
If you want to give h1 and h2 the same font size of 40px, then writing CSS separately like this:
h1 {
font-size: 40px;
}
h2 {
font-size: 40px;
}
is not efficient. It repeats the same code twice, making your CSS longer than needed.
The better way is to write the CSS for both selectors together, like this:
h1, h2 {
font-size: 40px;
}
This way, you write the style only once, and it applies to both h1 and h2, making your CSS shorter, cleaner, and easier to maintain.
Why does this matter for page speed?
When your CSS file is smaller and cleaner, the browser can download and process it faster. This means the webpage loads quicker and shows content sooner to users. On the other hand, repetitive and bulky CSS increases file size, which can slow down page load time and hurt the user experience.
So, writing efficient CSS not only helps you keep your code organized but also improves your website’s loading speed and performance.
6. Segmented CSS: Why and How to Use It?
Suppose you are making a website with five pages. It’s not a good idea to write all the CSS for all five pages in one single file. Instead, you should create separate CSS files for each page.
For example:
- CSS for the homepage
- CSS for the About Us page
- CSS for the Services page
- CSS for the Blog page
- CSS for the Contact Us page
By keeping the CSS separate for each page, when a user visits your website and clicks on a page, only the CSS for that specific page loads — not the CSS for all the pages. This makes your website faster and easier to maintain.
Example
homepage.css
/* homepage.css */
.header {
background-color: blue;
}
about.css
/* about.css */
.team-section {
font-size: 18px;
color: green;
}
services.css
/* services.css */
.service-item {
border: 1px solid #ccc;
padding: 20px;
}
blog.css
/* blog.css */
.post-title {
font-weight: bold;
font-size: 24px;
}
contact.css
/* contact.css */
.contact-form {
background-color: #f9f9f9;
padding: 30px;
}This way, your site loads only the CSS needed for each page, improving page speed and user experience.
7. Remove Unused CSS
Over time, projects accumulate unused selectors from old features or libraries. Removing unused CSS improves FID and LCP.
Tools to find unused CSS:
- Chrome Coverage (DevTools > Coverage)
- PurgeCSS / UnCSS
- Tailwind JIT (if using Tailwind CSS)
8. Use System Fonts or Font-Display
Custom web fonts can cause layout shifts and delays. Optimize by:
- Using system fonts for faster rendering.
- Adding
font-display: swap;in CSS to show fallback text while fonts load. - Preloading critical font files to avoid late shifts.
@font-face {
font-family: 'MyFont';
src: url('myfont.woff2') format('woff2');
font-display: swap;
}
9. Optimize Animations and Transitions
Poorly written CSS animations can cause CLS and increase CPU usage:
- Animate only transform and opacity (GPU-accelerated).
- Avoid animating layout properties like
width,height, ormargin. - Use
prefers-reduced-motionto respect user settings.
10. Break Down Large CSS into Smaller Chunks
If your site has multiple sections (e.g., blog, shop, dashboard), don’t link one big CSS file everywhere:
- Code-split styles per page or component.
- Load styles only when needed.
Modern frameworks like Next.js, Vue, and React support automatic CSS code-splitting.
11. Preload and Preconnect
Preloading ensures the browser starts fetching CSS files early. Preconnecting prepares the connection for CDN-hosted styles.
<link rel="preconnect" href="https://cdn.example.com">
<link rel="preload" href="/css/main.css" as="style">
12. Implement Proper Caching
Enable long-term caching for CSS files:
- Add versioning (e.g.,
style.v1.css) for cache busting. - Use
Cache-Controlheaders to allow browsers to reuse styles for repeat visitors.
13. Keep CSS Modular and Maintainable
A messy CSS architecture leads to duplication and bloat:
- Follow BEM (Block Element Modifier) or utility-first (Tailwind) approaches.
- Avoid deep nesting; keep selectors simple.
- Regularly audit styles during development.
14. Monitor Performance with Tools
Regularly check performance metrics:
- Lighthouse and PageSpeed Insights for Core Web Vitals scores.
- WebPageTest to analyze render-blocking CSS.
- Chrome DevTools to visualize CSS coverage and network waterfalls. Fix if any network load css error.
In short, always write your CSS in a clean and organized way. Avoid duplicating the same styles multiple times, and don’t put all the CSS for an entire website into a single file.
Instead, write maintainable and modular CSS by separating styles logically. This approach helps keep your code easy to read, debug, and update. It also improves website performance and makes teamwork easier when working with other developers.
