1kb Grid Tool
An Easy to Use Generator that Delivers the Perfect CSS File for Your Needs! Use it And You Won’t Need Another One!

Whenever a visitor loads a website, the request for its CSS file can sometimes take a significant amount of time, leading to delays in the rendering of its webpage. The reason behind this is that web browsers by default delay the page rendering, until the time they are done with loading, parsing and execution of all the CSS files they see referenced inside the header or < head > area of the webpage. They do this because it’s important for the correct calculation of the web page’s layout.

Unfortunately, this implies that any time there’s an extremely large CSS file, and it’s taking plenty of time to download, the users will have no option but to wait until the entire CSS file has been downloaded. It is only then that the browser will be able to start rendering the webpage.

As a good news, there is a certain technique which can help in optimizing the delivery of the CSS files, and lessen the adverse effects of such blocking. This method or technique is referred to as optimization of the critical rendering path.

Critical rendering path refers to the steps taken by a web browser for rendering of a web page. What we need here is the critical CSS or the minimum set of blocking cascading style sheet (CSS) required to make the webpage appear to the website visitors. (Any resource that may possibly block the webpage’s initial rendering is referred to as critical resource.) The main idea behind this process is to enable the website to show at least first screen’s worth of content to the website’s visitor (above the fold content) in the beginning. This content would be contained in the initial few TCP packets.

What happens is that the user is only able to see critical area of the webpage when he/she first loads up the page. Hence, the developer needs to ensure that only that much CSS gets loaded as is needed for rendering the top/critical area of the webpage. As regards the rest of the CSS, it can be loaded asynchronously and need not be worried about!

So, how do you go about determining what’s critical and what’s not? Determination of critical CSS for a webpage is a fairly complex process and will need you to walk through the DOM of the webpage. Once you’re done with that, you’ll need to figure out the list of different styles that need to be applied to every element in the initial view. Carrying out this process manually can be a pretty tedious affair, but there are several useful tools that can be used to do it automatically. Going into each one of those tools may be out of scope of this article, nevertheless, you should be aware that such tools exist and they can significantly improve the rendering speed of your webpages, with the use of critical CSS.

On a different note, you can make use of tools like 1kb grid, 960gs etc. for creating lightweight CSS grid structure for your websites.