Tag Archives: Cascading Style Sheets

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!

Optimizing CSS. Five simple steps!

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In the spirit of the optimization wave this post is about CSS optimization. There are some simple rules that you can apply. I’m pretty sure most of us have already been familiar with that list, but you never know.

1. Minify

As the JavaScript the CSS also can be minified. This only strips every character that makes the traffic bigger. As you know a well constructed and pretty looking CSS file consists of many new lines, tabs and spaces. Almost every software minifies the CSS by simply removing them. Some of the programs go even further with replacements of different parts of the code considered to be not efficient.

2. Use effective selectors

Some CSS selectors aren’t really efficient. Imagine something like: body div a just to describe only one specific link. That’s really bad. Better practice is to replace that line with something like a.my-class and to replace the a tag into the DOM with that class name. That will be far more effective. Actually if you’re wondering how to find such bad selectors, there’s a tool by Google called Page Speed that’s a Firebug’s plugin and can extract a list of all bad selectors.

3. Inheritance

CSS is really powerful when dealing with inheritance. That’s something that is not some clear but however really powerful. This technique is in the basics of the next rule.

4. Sprites

I’ve written already about CSS sprites. This is nothing new, but be careful when making a new site’s layout. CSS sprites spend you HTTP request and that’s rule number one according to Steve Souders’ list of optimization.

5. Separate logic

Sometimes developers put the site logic in only one file that become to large. Be aware of that. This is hard to maintain and you load things that you don’t need.

That’s a really short list of what you can do with CSS to speed the site up. I hope that can help someone when dealing with cascading style sheets.

CSS default position value

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position:absolute?

Recently I was working on a problem where some DOM elements inherited the absolute position from their ancestors. Well this is pretty rare, but however it happens from time to time. If you’re wandering, as I was, how to disable this and to call the default property value just stop hesitating. The default property is static. So you can simply write:

#element_id {
   position:static;
}

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.

Optimizing the web. Start with the images!

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Common question when speaking about web site optimization is: where should I start. As I mentioned before almost every technology used in the building of a web project can be improved. The bad news is that this improvement needs effort and when it comes to changing some code that’s already written that’s bad. The good news, as it exists, is that in the most cases most of the traffic of a site comes by images and/or other media and their optimization doesn’t have to deal with coding and can simply be optimized.

Optimize every image

The first thing that you can do to improve your site image is to optimize them. Sometimes the files you put on the site as they are JPEG, GIF and PNGs can be improved just by using some software that strips useless information from their headers and using various algorithms to smooth the similar pixels. As you may know in the case of PNG and GIF this is particularly natural. Stoyan Stefanov a lead Yahoo! developer is know as guru when it comes image optimization. You can check more detailed information about software and tools on his blog here. The reality is that you don’t need extra info into the images, as useless information about the camera, which is often setup into the image header, and when it comes to the web that’s really good. In fact according to some researches this can spend you more than 30% of traffic. Continue reading Optimizing the web. Start with the images! →