Traditionally, having a single CSS file was advantageous due to the speed boost it provided when using HTTP1.1.

However, with the majority of browsers now supporting HTTP2 as of March 2018, the landscape has changed. HTTP2 allows for simultaneous download of multiple resources and proactive resource pushing, making a single CSS file unnecessarily large. With careful planning, the only benefit seems to be coding convenience.

The most efficient design for optimal performance with HTTP2 would involve:

• Including core CSS in a single file for common styles shared across all pages.
• Separating page-specific CSS into individual files.
• Utilizing HTTP2 push for CSS to reduce wait time (using a cookie to prevent redundant pushes).
• Optionally prioritizing above-the-fold CSS for quick loading followed by loading the rest later (useful for low-bandwidth mobile devices).
• Loading additional CSS for the entire site or specific pages after the initial page load to expedite subsequent visits.

During the development process, I personally lean towards utilizing multiple CSS files as it simplifies management and debugging tasks. Yet, when it comes to deployment, my recommendation is to opt for a CSS minification tool such as YUI Compressor which will amalgamate all your CSS files into a single comprehensive file.

Optimizing your CSS for faster loading times is crucial for improving website performance. Using only one CSS file reduces the number of HTTP requests and speeds up page load times.

However, working with multiple smaller CSS files can make development easier, especially when organizing styles for different modules of your application..

There are benefits to both approaches, so why not take advantage of both worlds?

One solution is to develop using several small CSS files while implementing a build process that combines them into one centralized file.

• This makes development easier and more organized
• The build process can also minify the final CSS file for optimal performance
• Your application will need configuration settings to switch between multi-file mode and single-file mode
• In production, only use the combined big file for faster page loads

Some tools exist for combining CSS files at runtime instead of during build time, but be aware that this may consume more CPU resources. Implement caching mechanisms to avoid excessive regeneration of the combined file.

Why settle for one when you can have both?

You understand the importance of having multiple CSS files, but you also see the benefits of a single large file.

The key is finding a way to merge them seamlessly.

Imagine using a script like this:

<link rel="stylesheet" type="text/css" href="allcss.php?files=positions.css,buttons.css,copy.css" />

This clever script combines all your files into one, saving you time and effort.

It even keeps track of file modifications and only sends updated versions, reducing redundancy.

You get the best of both worlds - whether it's for CSS or JS.

While monolithic stylesheets do have numerous advantages (as outlined in other responses), there is a potential issue to be aware of when it comes to IE. Specifically, Internet Explorer has a restriction on the number of selectors it can read from a single stylesheet – capped at 4096 selectors. If your monolithic stylesheet exceeds this limit, splitting it into smaller files may be necessary. It's important to note that this limitation only affects IE users.

This particular constraint applies to all versions of Internet Explorer.

For more information, check out Ross Bruniges Blog and MSDN AddRule page.

There comes a moment when having multiple CSS files is more advantageous than just one.

For a website with over 1 million pages, where the average user may only visit around 5 of them, it would make sense to have a large stylesheet rather than trying to avoid an extra request per page load. Having a massive initial download can actually be counterproductive in this scenario.

If we take this argument to its extreme, it's like proposing that there should be a single mega stylesheet for the entire internet. That clearly doesn't make any sense.

The tipping point will vary for each website, depending on factors such as the amount of unique CSS per page, the total number of pages, and how many pages the average user interacts with regularly.

In my usual setup, I work with a few CSS files:

• One "global" CSS file that contains resets and global styles
• "Module"-specific CSS files for logically grouped pages (like every page in a checkout wizard)
• "Page"-specific CSS files for overrides on individual pages (or included in a block on the page itself)

I'm not overly worried about multiple page requests for CSS files. Most users have decent bandwidth, and I believe there are more impactful optimizations than combining all styles into one massive CSS file. The key is finding the right balance between speed and maintainability, and I tend to prioritize maintainability. I've heard good things about the YUI compressor though, so I might give it a try.

My personal preference is to use multiple CSS files because it allows for easy swapping of "skins" whenever needed. Having one large file can become unwieldy and difficult to handle. For example, if you wish to have blue backgrounds without changing the buttons, you can simply modify your backgrounds file without affecting other elements. This approach provides more flexibility and ease in managing CSS styles.

Consider checking out compass, an open source CSS authoring framework that is built on Sass. Compass offers support for features like variables, nesting, mixins, and imports. Imports can be particularly useful for consolidating multiple small CSS files into one to optimize performance and reduce HTTP requests. Additionally, Compass includes a library of pre-defined mixins designed to simplify handling cross-browser compatibility issues. Although Compass is written in Ruby, it is adaptable for use with various systems....

Here's a great method:

• Begin by creating a universal CSS file containing all common code
• Next, include specific page CSS within the same page, either within style tags or using the style attribute for each individual page

This approach results in just one CSS file containing all shared code alongside an HTML page. Additionally, although it's off-topic, consider encoding your images in base64 (which can also be done with JS and CSS files). This further reduces HTTP requests to just 1.

SASS and LESS offer a convenient solution to streamline the development process. By creating efficient component files that can be combined during compilation, developers can easily manage their styles. In SASS, developers have the option to switch off Compressed Mode for better readability during development and then switch it back on for production.

Learn more about SASS at http://sass-lang.com Explore LESS at

Ultimately, the goal is to have a single minified CSS file regardless of whether you choose SASS or LESS. This approach leads to fewer HTTP requests, reduced server load, and a more streamlined workflow.

One major benefit of consolidating CSS files into a single file is the improvement in transfer efficiency. With each HTTP request for a separate CSS file, there is additional bandwidth consumption due to the necessary HTTP header responses.

I have optimized my CSS delivery by serving it as a PHP file with the "text/css" mime type set in the HTTP header. This enables me to store multiple CSS files on the server and dynamically combine them into one when requested through PHP includes. As a result, all modern browsers interpret the .php file containing CSS code seamlessly as if it were a standard .css file.

To optimize performance, consider using a single CSS file and temporarily disabling sections by commenting them out as shown below:

/******** Navigation ************/
//css navigation styles

/******* End Navigation *********/


/******** Sidebar ************/
//css sidebar styles

/******* End Sidebar *********/

And so on...

For managing my CSS files, I rely on Jammit. This tool allows me to use multiple separate files for better organization and readability. With Jammit handling the grunt work of merging and optimizing files before deployment, I can easily transition from having numerous individual files during development to just one streamlined file in production.

While using bundled stylesheets can help save on page load performance, it can also slow down the browser's rendering of animations due to the excess amount of styles present. Even if these styles are not being used on the current page, the browser still has to process them.

For more information, check out:

Advantages of bundled stylesheets: - Improved page load performance

Disadvantages of bundled stylesheets: - Slower behavior leading to choppy scrolling, interactivity, and animations

Conclusion: To address both issues, it is recommended for production to bundle all css into a single file to reduce http requests. However, use javascript to extract only the necessary css for the current page and dynamically update the head with it.

To simplify the process of determining which shared components are required for each page and reduce complexity, it would be helpful to declare all the components used on that specific page, such as:

<style href="global.css" rel="stylesheet"/>
<body data-shared-css-components="x,y,z">