Tag Archives: html

CSS sprites. Go beyond the limits with base64!

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Why should I optimize CSS?

In fact how and why should I optimize CSS is the right question. Actually CSS is simply one ore more files loaded from the server to the client, usually a browser, with CSS specific rules that must be applied by the browser to the web page you’re seeing. That’s in general. Of course there are exceptions when CSS can be inline or added directly to the HTML tags, which is bad practice because thus the HTML markup becomes larger and even worse the browser cannot cache it and than load it quickly. In fact that’s why usually the CSS of a web page is put in one single file. Primary because that makes only one request to the server and in second hand because it can be cached by the browser.

Just because the nature of the CSS is that firstly it’s loaded and than executed one of the primary techniques of optimizing it is to make it smaller and therefore load faster. There are several methods of doing so. Enabling GZIP support of the web server and minifying the file are the most common ones. But one of the tricks you cannot optimizing just for second is using the so called CSS sprites.

CSS sprites

What are these? To answer this question I’ll simply try to give you an example. Let’s assume there are three CSS classes each one with its own background image. This makes four requests to the server. One for the CSS file and one per every background image. But what we’d like to achieve is to make less requests as we can. Than one of the things we can do is to make one single image and to change only the background-position CSS property to position it on the right place and to make it appear correctly.

Be careful! When you join all of the images into one single CSS sprite you may add one class with that background-image and every other class with only background-position property. Than every DOM element with that background must have both class names. Only than you can be sure the server will make two requests. One for the CSS file and one for the sprite.

base64 to encode images

In other hand most of the web projects are pretty big, and unfortunately it’s too difficult to make only one single sprite just because it’s too difficult to manage it after the project has become very large. That’s why mostly in the practice there are several sprites for the main components. But the problem is that again there are more HTTP requests.

Is there any way to make only one request?

Yes there is. Simply by converting your CSS sprite into a base64 encoded image. In breve base64 is an encoding where you can practically make any data into a string. Thus the image can be represented by a string containing the same information as the image. Hopefully most of the browser, except of course MSIE, does read the so called data urls, or:

<img src="data:image/png;base64,..... " />

and that’s enough to get started with base64 and the single request. The sprite has become a string!

CSS and base64

The natural question is now how to merge all this? You now have one CSS file with one or more sprites. Than you can convert them into a base64 encoded strings and put them all into the CSS.

There is a problem, of course, what happens with MSIE. As I said before MSIE doesn’t read base64 encoded images. Hopefully there is a solution described very well by Stoyan Stefanov in his blog post here.

Finally …

now there is only one request and everything works pretty fine. This technique can be really helpful to someone who’s trying to optimize the CSS performance to the limits.

CSS effective selector

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CSS optimization

Recently I posted an article about CSS optimization describing five simple steps you can do to speed up the page load time and the bowser execution time. One of the key features is to use effective selectors, but what exactly that means.

Parents and children

In CSS, after the name of cascading, there is a very powerful feature of inheritance and you can simply describe a child style by a selector which can be something like that:

div table tr td a { color: red; }

In reality is very, but very inefficient. Event it is a working example, the browser will find every anchor <a tag within the page than check if it’s child of a td, than tr and so on until the closing outer most div tag.

That’s why the browser is really hard to find every one of these tags just to apply a simple font color. What the big problem is that once you have thousands of tags in that page the browser starts to use CPU and the application starts to be irresponsive.

The solution

Of course there’s a simple solution, which can be described as transformation from inefficient to efficient selectors. Because the browser can find a tag way faster by a given ID or CLASS you can simply convert the code above with something like:

a.my-class { color: red; }

and than change a bit the markup with a tags with that specific class name. Which is a bit tricky, but speedups the performance a lot.

How can I find bad selectors?

Actually that is the big problem. Once you’re into the deep of web development the applications are so big, with so many CSS selectors and so many CSS rules that you simply cannot track that any more.

Hopefully there comes some tools that can describe you everything and point you the inefficient selectors. My personal choice is the Google’s Page Speed plugin, which can be installed to the Firebug on Mozilla Firefox. It can analyze the page and extract a list of inefficient and so called very inefficient selectors that must be fixed!

YouTube and Vimeo goes HTML5 with video tag usage! Catch them up!

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What better example than that coming both from YouTube and Vimeo. Although video tag is not supported except under Safari and Chrome, that’s the future everyone’s going to embed sooner or later.

And if these “big players” are going that way, don’t hesitate to follow them! HTML5 is really what we as web developers were waiting for so long and even all of the problems during its standardization process it’s really cool there will be tags like video.

What YouTube is doing today, perhaps will seem normal to everyone tomorrow. However there are some questions still with no answer, as where the flash possibility to add ads into the player is going?! But we’re about to see great things from these two sites!

Just check out these two links:

Youtube HTML5

Vimeo

What if your site doesn’t use all of the CSS selectors?

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Why my site doesn’t use all of the CSS however?

Well someone can ask how you can have CSS that contains selectors that aren’t used on the site. There are two reasons to happen and most of the cases both of them are true.

The first reason is that not all of the pages in a site need all of the selectors. Imagine large web based application with lines of CSS and one of the sites’ pages is the “about” page where you’ve only the header, the footer and some text. That’s my favorite example! In fact you don’t need to load the whole CSS file just to apply only few selectors for this page. In most of the cases this is the reason to have unused selectors.

The second reason is that during the development process most of the code become old and therefore unused. You start by writing some CSS selectors which after changing the requirements, and the layout are no longer used. But the fear to ruine the layout because some other page can break after the removal of some selectors make the CSS to grow and fill with unused code.

Now you can overcome this problem by simply using a software (JavaScript) that helps you determine which selectors are never used. Check out this brilliant solution called helium.

Faster HTML! Why not?

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Although I’ve read so many articles about web page optimization there’s not so much about optimizing HTML.

Why?

Maybe because nobody things that the HTML source of a page can be optimized or the optimization of it cannot bring some benefit to the page load experience. I don’t thing so. If something can be optimized, even if this does not give you so much, why you shouldn’t do it?

How to optimize such thing as HTML?

Well there are few things you should do and other that can speed up a little bit but you should not.

1. Enable gzip

What is gzip? Well in breve everything the server generates is sent back to the client in text format. You’ve to possibilities to send it. Either compressed or uncompressed. As you may guess the compressed format is a lot faster than uncompressed. In fact to make it work that way you’d need to enable gzip which is supported by the web server. In the case of Apache web server this can be done by enabling mod_deflate. Take a look of mod_deflated and mod_inflate. This two modules gives you the possibility to make your site a lot faster and the good news is that this is done without a single line change. The bad news, as always there’s a bad news, is that sometimes this cannot help a visitor, simply because his browser doesn’t support such corresponding with the server. According to a research I’ve read recently almost 15% of the web browsers doesn’t support gzip. Sometimes the reason is old browser versions, sometimes because the state policy doesn’t allow it. However this is the first thing you should do to speed up your HTML even it is not related directly to HTML scripts. By the way this will speed up everything which is sent back to the client, especially CSS and JavaScript files and in the case of JavaScript this can improve dramatically the user experience. Continue reading Faster HTML! Why not? →