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6 Effective Ways to Remove Unused CSS

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.

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:

  • Overly Generic Styling: Applying broad styles that are not specific to particular elements can lead to unused CSS. These styles might be intended for certain elements but end up being applied to fewer elements than anticipated.

  • Redundant Styles: Duplicate or redundant CSS rules, such as styling properties that are overridden by later declarations, can result in unused CSS.

  • Framework or Library Bloat: Using CSS frameworks or libraries often includes a significant amount of pre-written styles that may not all be utilized in a project. This can lead to a buildup of unused CSS.

  • Dynamic Content: Websites with dynamic content may only utilize certain styles under specific conditions or for certain pages. As a result, CSS rules designed for all scenarios may go unused.

  • Evolution of Design: As a project evolves, design requirements may change, leading to styles that are no longer needed. However, these unused styles may remain in the CSS files if not regularly reviewed and removed.

  • Unused Selectors: CSS selectors targeting elements that no longer exist or are no longer used in the HTML markup can result in unused CSS rules.

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

Removing unused CSS is important for several reasons:

  • Performance Optimization: Unused CSS adds unnecessary file size to your stylesheets, increasing page load times. By removing unused CSS, you reduce the amount of data that needs to be downloaded, leading to faster page load speeds and improved performance.

  • Bandwidth Savings: Smaller CSS files result in reduced bandwidth usage, benefiting both website visitors and server resources. This is particularly crucial for users with limited data plans or slower internet connections.

  • Improved Rendering Speed: Browsers must parse and apply CSS styles to render web pages. Removing unused CSS reduces the amount of parsing and computation required, resulting in faster rendering times and smoother user experiences.

  • Simplified Maintenance: A leaner CSS codebase is easier to maintain and update. By eliminating unused styles, you reduce complexity and make it easier to identify and address styling issues or make design changes in the future.

  • Enhanced Code Quality: Removing unused CSS promotes cleaner and more efficient code practices. It encourages developers to write CSS that is purposeful and targeted, leading to better code quality and easier collaboration within development teams.

  • Better SEO: Google’s Page Experience algorithm considers page speed as a ranking factor. By optimizing CSS and improving page load times, you enhance user experience and potentially improve your website’s search engine ranking.

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How 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.

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.

This method requires attention to detail and knowledge of CSS selectors and browser developer tools. Use this guide with caution, as mistakes can lead to unexpected website behavior. Here are some common step for you to identify unused CSS manually:

  • Open the webpage you want to analyze

  • Open the Developer Tools: Press F12 (Windows/Linux) or Command + Option + I (Mac).

  • Navigate to the “Elements” tab: This tab displays the HTML structure of the page.

  • In the “Elements” tab, find the element you’re interested in (e.g., a button, navigation bar)

  • Right-click on the element and choose “Inspect” to open the detailed element information.

  • Look for the “Styles” panel within the developer tools. This will show all CSS rules applied to the selected element, categorized by origin (inline styles, stylesheets, etc.).

Check manually

  • Focus on non-inherited styles: These are styles explicitly defined for the specific element and not inherited from its parent elements.

  • Examine each non-inherited style: Analyze the property-value pairs. Look for:

    • Properties visually affecting the element: These are likely used styles. Examples include color, font-size, background-color, padding, etc.

    • Properties with seemingly no visual impact: These might be unused. Examples include display: none; visibility: hidden; or properties with default values.

  • Click the checkbox next to a specific style rule to temporarily disable it. If disabling the rule doesn’t change the element’s appearance, it’s likely unused.

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.

Consider automated tools and services

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

PurifyCSS Online Website Unused CSS Check

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.

Use web performance tracking tools

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

Google Lighthouse unused CSS detection

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.

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How 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.

Once unused CSS has been identified, there are several ways to remove it.

Manual Removal

Manual removal of unused CSS involves the following steps:

  • Backup Your CSS Files: Before making any changes, create a backup of your CSS files to ensure that you can revert to the original state if needed. This provides a safety net in case any unintended changes occur during the removal process.

  • Open CSS Files for Editing: Open the CSS files containing the identified unused CSS rules in a text editor or integrated development environment (IDE). Navigate to the sections of the file where the unused styles are located.

Open CSS Files for Editing

  • Manually Remove Unused CSS: Review each unused CSS rule and remove it from the stylesheet. This can be done by deleting the entire rule or comment it out if you want to keep a record of the removed styles for future reference.

  • Test Changes: After removing the unused CSS, thoroughly test your website to ensure that it still looks and functions as intended. Check different pages, layouts, and interactions to verify that no styling issues have been introduced by the removal of unused styles.

  • Repeat Process: Repeat the process for all identified unused CSS rules in your codebase. Depending on the size of your project and the amount of unused CSS, this may take some time, so be patient and methodical in your approach.

Automated Tools

Several tools are available for this task, each with its own features and complexities. Here are some popular options:

  • UnCSS: A popular online tool for removing unused CSS. It allows uploading your CSS files and provides an optimized, cleaned version.

  • PurifyCSS: An open-source JavaScript library that integrates with build tools like Gulp and Webpack. It analyzes your HTML and removes unused CSS selectors.

  • PostCSS UnCSS: A PostCSS plugin that works similarly to PurifyCSS.

  • CSSnano: A popular CSS minifier that includes an option to remove unused CSS selectors.

Most automated tools work well when integrated into your build process. This allows for automatic cleaning of CSS during development and deployment. Here’s a general workflow:

  • Install the chosen tool: Follow instructions based on the chosen tool (e.g., npm install for JavaScript libraries). Configure the tool: Specify the HTML files, CSS files, and any specific options the tool offers.

  • Run the tool: Integrate it into your build process using build tools like Gulp or Webpack. Alternatively, online tools provide direct upload and removal options.

Plase note that Automated tools can sometimes incorrectly mark used styles as unused. Always test your website thoroughly after using any tool to ensure functionality is not compromised. Ensure your CSS selectors are specific enough to target the intended elements. Overly generic selectors might lead to unexpected removal of used styles.

CSS Preprocessor Features

OCSS Preprocessor

CSS Preprocessors like Sass and LESS offer features that can assist in reducing unused CSS, but they don’t directly remove unused styles like the automated tools. Instead, they provide mechanisms to improve code organization and maintainability, which indirectly helps in reducing unused styles:

  • Prevent redundancy: Use variables and mixins to centralize common styles, reducing duplicate declarations and potential unused styles.

  • Organize code: Leverage nesting and import management to structure your CSS logically, making unused styles easier to identify within specific sections.

  • Conditional imports: Utilize conditional statements (if available) to import styles based on specific conditions, preventing unnecessary styles from loading.

  • Combine with dedicated tools: While preprocessors don’t directly remove unused CSS, they can significantly improve code organization and maintainability. Pair them with automated tools like PurifyCSS for optimal results.

CSS Framework Customization

While CSS frameworks like Bootstrap offer great functionalities, they often come with a lot of unused styles. Here’s how to use framework customization to tackle this:

Utilize the framework’s built-in customization tools: Many frameworks offer options to remove unused components or styles directly. For example:

  • Bootstrap: Bootstrap provides a “Customize” tool where you can select only the components you need and download a custom CSS file.

  • Tailwind CSS: Tailwind’s utility-first approach allows you to select only the specific utilities you use in your code, minimizing unused styles.

Leverage preprocessor features (indirectly helps):

  • Organize code: Use variables, mixins, nesting, and import management to structure your framework styles logically.

  • Override framework styles: If needed, use your preprocessor to selectively override specific framework styles with your own custom styles, reducing unnecessary elements from the framework.

Consider alternative approaches:

  • Use a smaller framework: If your project has specific needs, explore smaller, more focused frameworks that align better with your requirements, potentially reducing the amount of unused CSS.

  • Build your own styles: For projects with unique needs, consider building your own custom CSS from scratch, ensuring complete control over what styles are included.

Code Splitting and Tree Shaking

Code Splitting

While code splitting and tree shaking are powerful techniques for optimizing JavaScript code, they don’t directly apply to removing unused CSS. These functionalities primarily target JavaScript files and functionalities.

  • Code Splitting: This technique divides your JavaScript code into smaller chunks that are loaded on demand, based on user interaction or specific sections of your website. This reduces the initial load time by only loading the necessary code for the current view, improving website performance.

  • Tree Shaking: This process removes unused code (dead code) within JavaScript modules during the bundling process. This helps eliminate unnecessary code that is not imported or referenced within your application, further reducing the overall JavaScript bundle size.

Therefore, these techniques won’t directly impact CSS, as CSS styles are generally treated separately during web page rendering.

Conclusion

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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With over a decade of experience crafting innovative tech solutions for ecommerce businesses built on Magento, Jacker is the mastermind behind our secure and well-functioned extensions. With his expertise in building user-friendly interfaces and robust back-end systems, Mageplaza was able to deliver exceptional Magento solutions and services for over 122K+ customers around the world.
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