How to remove unused CSS? 6 Tips to apply.

Experienced E-commerce Agency for Magento/ Adobe Commerce/ Shopify/ Shopware Development

Every website needs cascading style sheets (CSS). This is an essential tool to assist businesses in painting a picture of how elements should be rendered on screen, paper, speech, or other media.

An inefficient and unused cascading style sheet can negatively impact a website’s performance. This can be listed as a slower load time, an increase in parsing time, a rise in maintenance complexity, and a lot more problems.

To mitigate the impact of unused CSS on website performance, the article below will provide businesses with 6 tips to remove unused CSS and boost their website performance.

Table of Contents

What are unused Cascading Style Sheets (CSS)?

Unused CSS refers to the CSS code not utilized or applied to any elements of a page website but still displayed on a web page’s style sheet. This is an unnecessary element that doesn’t benefit a web page. Opposingly, it can make website performance less efficient.

Unused CSS definition

Unused CSS negatively impacts website performance because even though this unused code doesn’t affect the appearance and behavior of the web page, the browser still needs to download and process it.

As a result, to optimize a website, businesses should prioritize identifying and removing unused CSS.

What causes unused CSS?

There are various reasons why unused CSS occurs, below are 3 most common reasons:

  • Iterative development: The website will witness changes and updates throughout the iterative development process. Certain styles and elements may become outdated or redundant as the design evolves. An unused CSS will appear if the associated rules are not cleaned or eliminated.

  • Collaboration: In a large project requiring many teams and developers, developers are in charge of various website fragments independently. As a result, adding new styles or duplicating existing ones will appear and lead to unused CSS when there is a lack of integration or cleanup.

  • Frameworks and templates: Most CSS frameworks and templates are designed to be suitable for many use cases, and they often come with an all-inclusive set of styles and components. However, some styles and components may be unnecessary for a specific project. As a result, unused CSS will occur if the entire framework or template is being used without customization or if only specific parts of the template are utilized.

Why should you remove unused CSS?

Unused CSS is the main factor that slows the page’s loading time and can negatively affect a website’s performance. It’s crucial to address and fix the unused CSS issues because if unused CSS is on the page, the browser will have to take a significant amount of time to download, analyze, and display it.

Unused CSS can slower web loading time

This holds particularly true for the CSS above the fold, which is the crucial content visible on the page when it loads. When ensuring a fast render, the most important content will be able to appear quickly on the website; thus, users can interact with the page more promptly.

As an additional performance benefit, when removing all the unused CSS, businesses boost the website speed and provide users with an excellent online experience.

5 Steps to identify unused CSS Files

The first and foremost thing businesses have to do before removing unused CSS in a website code base is to identify and have a specific understanding of the problems.

Here are 5 steps you can follow to make identifying unused CSS files easier and more efficient.

Step 1. Check manually

One of the most efficient solutions to identify unused CSS files is to track the CSS codebase, analyzing each CSS rule and determining which element will utilize on the website through a manual review process.

Even though this approach may require businesses to carefully inspect and understand the website’s structure and styling, it can be suitable and effective for small projects or specific sections of a codebase.

Step 2. Utilize CSS linting tools

A CSS linting tool is an ideal software that helps businesses to recognize possible errors, deviations from recommended methods, and any problems related to code quality.

This tool enables businesses to maintain a constant standard, enhance the ease of maintenance and detect common CSS code errors. Many CSS lining tools, namely Stylelint or CSSLint - for example, play an essential role in helping businesses to identify potential CSS code issues, including unused CSS.

These tools examine CSS files using pre-established rules or configurations and generate reports reviewing unused styles, duplicate rules, or other prevalent CSS code quality problems.

Step 3. Use browser developer tools

Browser developer tools, or so-called Browser DevTools, are a robust suite of built-in developer tools for every modern website browser, such as Chrome DevTools or Firefox Developer Tools.

These tools can utilize many tasks, including observing the loading of HTML, CSS, and JavaScript in real-time as well as indicating which assets are requested on the page and the loading time they require.

Browser developer tools can help to identify unused CSS

More than that, these tools can detect styles that are not applied to any element and then assist in identifying unused CSS by analyzing CSS rules and their attached elements. As a result, browser developer tools are highly important in finding and fixing unused codes.

Step 4. Consider automated tools and services

Automated tools and services, including PurifyCSS, UnCSS, or UnusedCSS, are specific tools that mainly focus on finding unused CSS.

Through a process of examining the website’s HTML structure and CSS, then deciding which styles will be associated with which elements on the website, these tools will provide a visualized analysis that points out unused CSS selectors, properties, or rules.

With the help of those automated tools and services, businesses will be able to detect and remove unused CSS more quickly and efficiently.

Step 5. Use web performance tracking tools

Another valuable solution to recognizing and addressing unused CSS problems is using web performance tracking tools.

Businesses can get detailed information and insights about unused CSS through many standard web performance tracking tools, namely Google Lighthouse or WebPageTest.

These tools provide businesses with an analysis of their website’s performance. Besides, you’ll see the outline and recommendation on optimizing CSS, along with unused style identification signs.

6 Prominent tips to remove unused CSS

Unused CSS can undoubtedly negatively impact website performance in many aspects, such as slow loading time, decrease in caching efficiency, less responsive web performance, and bad user experience.

For this reason, businesses should prioritize identifying and removing unused CSS problems. Here are 6 prominent tips to remove unused CSS that companies can apply to boost their website performance.

1. Identify unused CSS

If you want to find the best approach to tackle unused CSS issues on your website, the first and foremost thing you have to do is identify and understand unused CSS problems.

There are many methods that businesses can utilize to recognize unused CSS styles, selectors, and rules in the codebase, faster and easier, such as manual code review, browser developer tools, or automated tools and services.

By identifying unused CSS styles, selectors, and rules in the website’s codebase, you will have well-informed information about the root causes of these problems. Hence, finding the most efficient and suitable decision to solve the problem.

2. Create a backup

Changing unused CSS files is a must when recognizing any root causes for these issues. However, it is also advisable to create a backup of CSS files or utilize a version control system before tackling these unused CSS problems.

Preparing a good precautionary measure will ensure that when there are some mistakes or failures in the modification process, you will have the chance to revert to the previous version to redo it if necessary.

Creating a backup means having support plans, this will help you to be prepared if there are any unexpected errors and reduce the risk of failing, less time-consuming in the modification process.

3. Update CSS code regularly

Reviewing and cleaning up the CSS codebase frequently is also advisable when protecting your website from unused CSS code issues. Over time, each project does not stay the same; it may change and develops.

Update CSS code regularly may help reduce unused CSS

As a result, many styles that used to be suitable may become useless or outdated. By tracking the CSS codebase regularly, you will be more likely to recognize which file is inappropriate and remove it on time.

This is one of the best practices for you to keep your codebase lean and maintain optimal performance.

4. Test thoroughly

Thorough testing is a required process once you have eliminated unused CSS. In this testing stage, you will be able to ensure that the desired styles and layouts for the website remain unchanged.

Furthermore, testing thoroughly can help you track unintended side effects or missing styles that may have been unintentionally removed.

It is essential to perform comprehensive testing on the website after removing unused CSS because this will make the removing unused CSS process more accomplished.

5. Integrate matching styles

Another essential tip that can help to remove unused CSS is to search for similar or unneeded CSS rules and then merge them. This is because when multiple CSS rules attain similar styling effects, this can lead to duplicate styles, resulting in unnecessary code.

If the same styles are consolidated into one rule, you can remove redundancy and make the codebase more efficient and concise.

Overall, integrating matching styles helps clarify the CSS code, enhance maintainability, and accurately identify unused CSS.

6. Optimize build process

If you are using a build process or task runner, incorporating CSS optimization gadgets or plugins may be a great consideration to help you eliminate unused CSS automatically during the build process.

This can assist in clarifying the process of reducing unused CSS and ensure a systematic elimination of redundant styles.

Optimizing the build process will be very helpful in automating the removal of unused CSS, maintaining constancy, enhancing web performance, and boosting overall development efficiency.


Undeniably, unused CSS can negatively impact website performance, such as longer parsing and rending time, unnecessary network requests, cache inefficiency, and more.

Consequently, businesses should focus on tracking, identifying, and improving unused CSS problems to prevent website performance from deteriorating. With the 6 tips above, removing unused CSS will be easier and less time-consuming.

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Vinh Jacker
Hello, I'm the Chief Technology Officer of Mageplaza, and I am thrilled to share my story with you. My deep love and passion for technology have fueled my journey as a professional coder and an ultra-marathon runner. Over the past decade, I have accumulated extensive experience and honed my expertise in PHP development.
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