This is a long shot, but is there a tool available that optimizes CSS selectors by removing unneeded specificity?
I find that when I write CSS, I deliberately make my selectors more specific than necessary to avoid conflicts and for quasi-documentation.
It would be great if there were a tool that could analyze a given group of rules, determine their "uniqueness" in terms of overlap with other rules, and then strip away any unnecessary specificity.
I can't even begin to imagine how a tool developer would approach all of the scenarios this would require, but I've been blown away by others' ingenuities in this area before and figured it was worth asking.
Update:
I've added a bounty to this question, and the more I think about it, the more I realize how valuable a CSS Specificity Filter would be.
For example, when working with Nested Rules/Selectors in Sass and LESS, excessive nesting is a common and well-known antipattern that can easily lead to overly specific selectors.
There's a good illustration of this in the excellent TutsPlus course Maintainable CSS with Sass and Compass:
body {
div.container {
p {
a {
color: purple;
}
}
}
}
Sass will follow these nesting instructions and produce the following CSS output, raising no objection to any unneeded specificity:
body div.container p a {
color: purple;
}
If a Specificity Filter did/does exist, however, it would create potential benefits for CSS developers:
You could organize your stylesheets as a 1:1 mapping of the DOM, similar to what you see when you examine style rules in Firebug and Chrome Dev Tools. A smart editor/IDE could auto-populate styles for DOM elements with shared styles/classes. That redundancy would then, of course, be filtered out by the Specificity Filter/Optimizer.
Stylesheets could have their structure pre-populated by a tool that scans the DOM and translates it to CSS selectors/rules. This means a developer would only need to update the HTML; the CSS "tree" would be kept in sync to reflect the current state of the DOM. A smart editor would let you jump to the CSS definition for an element/class for styling -- or even make its style rules visible in a separate panel.
In a way, this almost seems like a step backward - like a feature you'd find in Dreamweaver or WebAssist to help newbs learn CSS. But the basic idea of a CSS selector optimization tool seems like a no brainer, and the type of workflow automation I've described would be the logical next step -- and the catalyst would be the Specificity Filter.
I looked into some of the better-known CSS editors and web IDEs, but haven't found anything offering this type of functionality beyond targeting a single element and generating a selector for it.
Update 2: CSS Selector Performance
In response to Spliff's comment, here are two great articles on CSS selector performance:
Performance Impact of CSS Selectors by Steve Souders
Efficiently Rendering CSS by Chris Coyier
Both agree that micro-optimizing CSS isn't worth the effort, but that over-qualified descendant selectors are "an efficiency disaster." I haven't benchmarked yet myself, but suspect that the kind of "DOM Mapping" approach I'm suggesting would cause a performance hit without an optimization step, either manual or automated.
Related Questions, Links, and Tools:
Points in CSS Specificity
Tool to See CSS Specificity
Tool for Cleaning Up CSS
Order by CSS Specificity
Top 5 Mistakes of Massive CSS
Google: Efficient CSS Selectors
Procssor
Clean CSS
CSS Tidy
You could attempt to take a different approach, try to write your selectors as small (low specificity) as possible. and only make them more specific when needed.
With that way of working you don't need a tool.
Just going to throw this out there-- it doesn't 'answer' your question,but it's a tool I like to spread the word about for people who do a lot of css programming: Firebug.
If you're not familiar with it, it's a tool for web browsers. You pull up your page once it's installed, right click and select 'Inspect Element.' It will show you all css affecting different elements on your page, and is useful for creating clean, precise css code. Also it makes it easier to see instant updates on what your page would look like with slight modifications. It will inform you of useless css code that's being overridden by other css code.
ALSO! Firebug now is available for almost all browsers. Not just Firefox. Personally, I'm partial to using it in Chrome.
We really can't do without specificity because it is the only thing that saves you when you have two or more rules colliding. Specificity brings sanity to the whole jumbled CSS rule, so it is more of a blessing than curse. Some of the stuff you talked about, like the CSS selector, can be done using Firefox/Firebug. I'm more disturbed by browser compatibility.
Actually there's a way you can do this using HTML5 and CSS3. The standard technique is to specify elements using the HTML 5 attribute "data-" and then do CSS selection for this attribute. This isn't the purpose of the attributes, but you can customly specify some elements that you can use to even switch the theme of a site.
So, for example, you can end up creating your specificity filters manually in CSS, by specifying
<b data-specificity=2>test</b>
where data-specificity only matches to parents above.
UPDATE:
Alright, so for example, let's say you have a paragraph class, but you want to specify which parent, or how many parents the paragraph can inherit properties from. You would use rules for each potential parent that can be inherited from:
p[data-specificity="1"]{
color:red;
font-family:verdana;
text-decoration:underline;
}
p[data-specificity="2"]{
color:black;
font-family:arial;
}
div.container > *[data-specificity="2"] {
font-family:impact;
color:blue;
text-decoration:underline;
}
So these rules mean that any p tag which is a direct child of the div container and has specificity 2, is allowed to inherit properties from the div container. The blue color of the div gets inherited by the p with data-specificity 2.
Here's a JSFiddle where you can see this!
The idea is that like this, using HTML5, you can control exactly which elements are allowed to inherit which properties. It's a lot of extra code to write (for both child and parent elements) but you can use this to get rid of some unnecessary specificity
I've never actually seen anyone use this method in practice, I pretty much just cooked it up for you, but I think it could be very useful, what do you think ?
I need to do this more generally, but a fine current example is my two menus. I have two menu classes, horizontal-menu and vertical-menu, and two sets of rules for elements like ul, li, and a under these classes. Many of these rules have things in common, like the color value for a elements. I would like to refactor the common rules and values into a 'super-class' called menu, and the have only override values in my horizontal-menu and vertical-menu classes. Is there a tool (besides the tool asking this question) that can help me with this?
The best tool for this kind of problem is Compass, a framework for defining rules which are then compiled into css for use in production. It allows you to define variables in much the same way as an imperative language.
It also has other helpful concepts such as mixins which allow the definition of a set of css properties which would be regularly used together, such that you can include that block of properties in multiple standard CSS rules. The power being that you can then edit that mixin in one place, changing the properties and having that change propagate to any CSS rule in which the mixin has been used.
I discovered Compass, and learnt how it should be used thanks, to a screencast by Chris Coyier at CSS Tricks
The only problem in this case (and most cases in fact) is that you really have to start from scratch with Compass, or find a way of integrating its work-flow into your existing one.
You may want to give csscss a shot. I wrote it in order to have an idea of how much I'm repeating myself in my own stylesheets. I'm obviously biased, but a number of people have found it helpful too. SASS, LESS, and Compass support are baked in.
Another great tool is helium which is a javascript tool that runs in the browser and lets you know of any unused rules.
When I see website starter code and examples, the CSS is always in a separate file, named something like "main.css", "default.css", or "Site.css". However, when I'm coding up a page, I'm often tempted to throw the CSS in-line with a DOM element, such as by setting "float: right" on an image. I get the feeling that this is "bad coding", since it's so rarely done in examples.
I understand that if the style will be applied to multiple objects, it's wise to follow "Don't Repeat Yourself" (DRY) and assign it to a CSS class to be referenced by each element. However, if I won't be repeating the CSS on another element, why not in-line the CSS as I write the HTML?
The question: Is using in-line CSS considered bad, even if it will only be used on that element? If so, why?
Example (is this bad?):
<img src="myimage.gif" style="float:right" />
Having to change 100 lines of code when you want to make the site look different. That may not apply in your example, but if you're using inline css for things like
<div style ="font-size:larger; text-align:center; font-weight:bold">
on each page to denote a page header, it would be a lot easier to maintain as
<div class="pageheader">
if the pageheader is defined in a single stylesheet so that if you want to change how a page header looks across the entire site, you change the css in one place.
However, I'll be a heretic and say that in your example, I see no problem. You're targeting the behavior of a single image, which probably has to look right on a single page, so putting the actual css in a stylesheet would probably be overkill.
The advantage for having a different css file are
Easy to maintain your html page
Change to the Look and feel will be easy and you can have support for many themes on your pages.
Your css file will be cached on the browser side. So you will contribute a little on internet traffic by not loading some kbs of data every time a the page is refreshed or user navigates your site.
The html5 approach to fast css prototyping
or: <style> tags are no longer just for the head any more!
Hacking CSS
Let's say you're debugging, and want to modify your page-css, make a certain section only look better. Instead of creating your styles inline the quick and dirty and un-maintainable way, you can do what I do these days and take a staged approach.
No inline style attribute
Never create your css inline, by which I mean: <element style='color:red'> or even <img style='float:right'> It's very convenient, but doesn't reflect actual selector specificity in a real css file later, and if you keep it, you'll regret the maintenance load later.
Prototype with <style> instead
Where you would have used inline css, instead use in-page <style> elements. Try that out! It works fine in all browsers, so is great for testing, yet allows you to gracefully move such css out to your global css files whenever you want/need to! ( *just be aware that the selectors will only have page-level specificity, instead of site-level specificity, so be wary of being too general) Just as clean as in your css files:
<style>
.avatar-image{
float:right
}
.faq .warning{
color:crimson;
}
p{
border-left:thin medium blue;
// this general of a selector would be very bad, though.
// so be aware of what'll happen to general selectors if they go
// global
}
</style>
Refactoring other people's inline css
Sometimes you're not even the problem, and you're dealing with someone else's inline css, and you have to refactor it. This is another great use for the <style> in page, so that you can directly strip the inline css and immediate place it right on the page in classes or ids or selectors while you're refactoring. If you are careful enough with your selectors as you go, you can then move the final result to the global css file at the end with just a copy & paste.
It's a little hard to transfer every bit of css immediately to the global css file, but with in-page <style> elements, we now have alternatives.
In addition to other answers.... Internationalization.
Depending of the language of the content - you often need to adapt the styling of an element.
One obvious example would be right-to-left languages.
Let's say you used your code:
<img src="myimage.gif" style="float:right" />
Now say you want your website to support rtl languages - you would need:
<img src="myimage.gif" style="float:left" />
So now, if you want to support both languages, there's no way to assign a value to float using inline styling.
With CSS this is easily taken care of with the lang attribute
So you could do something like this:
img {
float:right;
}
html[lang="he"] img { /* Hebrew. or.. lang="ar" for Arabic etc */
float:left;
}
Demo
Inline CSS will always, always win in precedence over any linked-stylesheet CSS. This can cause enormous headache for you if and when you go and write a proper cascading stylesheet, and your properties aren't applying correctly.
It also hurts your application semantically: CSS is about separating presentation from markup. When you tangle the two together, things get much more difficult to understand and maintain. It's a similar principle as separating database code from your controller code on the server side of things.
Finally, imagine that you have 20 of those image tags. What happens when you decide that they should be floated left?
This only applies to handwritten code. If you generate code, I think that it's okay to use inline styles here and then, especially in cases where elements and controls need special treatment.
DRY is a good concept for handwritten code, but in machine-generated code, I opt for "Law of Demeter": "What belongs together, must stay together". It's easier to manipulate code that generates Style tags than to edit a global style a second time in a different and "remote" CSS file.
The answer to your question: it depends...
Using inline CSS is much harder to maintain.
For every property you want to change, using inline CSS requires you to look for the corresponding HTML code, instead of just looking inside clearly-defined and hopefully well-structured CSS files.
The whole point of CSS is to separate content from its presentation. So in your example you are mixing content with presentation and this may be "considered harmful".
In addition to the other answers, another concern is that it violates the recommended Content Security Policy from MDN, https://infosec.mozilla.org/guidelines/web_security#content-security-policy
The justification they use is that inline javascript is harmful, XSS, etc., but it doesn't justify why inline styles should also be disabled. Maybe someone can comment as to why, but until then, I'll just rely on appeal-to-authority and claim: it's a security best practice to avoid inline styles.
Code how you like to code, but if you are passing it on to someone else it is best to use what everyone else does. There are reasons for CSS, then there are reasons for inline. I use both, because it is just easier for me. Using CSS is wonderful when you have a lot of the same repetition. However, when you have a bunch of different elements with different properties then that becomes a problem. One instance for me is when I am positioning elements on a page. Each element as a different top and left property. If I put that all in a CSS that would really annoy the mess out of me going between the html and css page. So CSS is great when you want everything to have the same font, color, hover effect, etc. But when everything has a different position adding a CSS instance for each element can really be a pain. That is just my opinion though. CSS really has great relevance in larger applications when your having to dig through code. Use Mozilla web developer plugin and it will help you find the elements IDs and Classes.
I think that even if you want to have a certain style for one element, you have to consider the possibility that you may want to apply the same style on the same element on different pages.
One day somebody may ask to change or add more stylistic changes to the same element on every page. If you had the styles defined in an external CSS file, you would only have to make changes there, and it would be reflected in the same element in all of the pages, thus saving you a headache. :-)
Even if you only use the style once as in this example you've still mixed CONTENT and DESIGN. Lookup "Separation of concerns".
Using inline styles violates the Separation of Concerns principle, as you are effectively mixing markup and style in the same source file. It also, in most cases, violates the DRY (Don't Repeat Yourself) principle since they are only applicable to a single element, whereas a class can be applied to several of them (and even be extended through the magic of CSS rules!).
Furthermore, judicious use of classes is beneficial if your site contains scripting. For example, several popular JavaScript libs such as JQuery depend heavily on classes as selectors.
Finally, using classes adds additional clarity to your DOM, since you effectively have descriptors telling you what kind of element a given node in it is. For example:
<div class="header-row">It's a row!</div>
Is a lot more expressive than:
<div style="height: 80px; width: 100%;">It's...something?</div>
Inline CSS is good for machine-generated code, and can be fine when most visitors only browse one page on a site, but one thing it can't do is handle media queries to allow different looks for screens of different sizes. For that, you need to include the CSS either in an external style sheet or in an internal style tag.
In-page css is the in-thing at the moment because Google rates it as giving a better user experience than css loaded from a separate file. A possible solution is to put the css in a text file, load it on the fly with php, and output it into the document head. In the <head> section include this:
<head> ...
<?php
$codestring = file_get_contents("styles/style1.txt");
echo "<style>" . $codestring . "</style>";
?>
... </head>
Put the required css in styles/style1.txt and it'll get spat out in the <head> section of your document. This way, you'll have in-page css with the benefit of using a style template, style1.txt, which can be shared by any and all pages, allowing site-wide style changes to be made via only that one file. Furthermore, this method doesn't require the browser to request separate css files from the server (thus minimising retrieval / rendering time), since everything is delivered at once by php.
Having implemented this, individual one-time-only styles can be manually coded where needed.
According to the AMP HTML Specification it is necessary to put CSS in your HTML file (vs an external stylesheet) for performance purposes. This does not mean inline CSS but they do specify no external stylesheets.
An incomplete list of optimizations such a serving system might do is:
Replace image references with images sized to the viewer’s viewport.
Inline images that are visible above the fold.
Inline CSS variables.
Preload extended components.
Minify HTML and CSS.
Personally, I think the hatred of inline css is just ridiculous. Hardcore cult behaviour, people just sheepishly repeat "Separation of concerns!". Yes, there are times where if there is a repeating element and you will need repeated styling to use a class targeted from a CSS file, but most of the time it improves speed of development and CLARITY OF CODE to put the style inline, it's great if I can look at the code and see that there is a custom margin height, it helps me picture the HTML document as a whole, instead of some named class that gives me little insight into which styles will be applied.
So I will be the contrarian here and say that inline css is great and that people who scream at you for using it are just following what they have been told without actually giving it any original unbiased consideration.
Even though I totally agree with all the answers given above that writing CSS in a separate file is always better from code reusability, maintainability, better separation of concerns there are many scenarios where people prefer inline CSS in their production code -
The external CSS file causes one extra HTTP call to browser and thus additional latency. Instead if the CSS is inserted inline then browser can start parsing it right away. Especially over SSL HTTP calls are more costly and adds up additional latency to the page. There are many tools available that helps to generate static HTML pages (or page snippet) by inserting external CSS files as inline code. These tools are used at the Build and Release phase where the production binary is generated. This way we get all the advantages of external CSS and also the page becomes faster.
In addition to other answers, you cant target the pseudo-classes or pseudo-elements in inline CSS
We have created a template-driven artifact generator that provides an include file capability for any kind of text artifact -- HTML, XML, computer languages, unstructured text, DSV, etc. (E.g., it's great for handling common Web or manual page headers and footers without scripting.)
Once you have that and use it to provide "style" tags inside your "head" tag, the "separation of concerns" argument goes away, to be replaced by "we have to regenerate after every change to the template" and "we have to debug the template from what it generates". Those gripes have been around since the first computer language to get a preprocessor (or someone started using M4).
On balance, we think the meta-izing capability of either a CSS file or "style" tags is cleaner and less error-prone than element-level styling. But it does require some professional judgment, so newbies and scatterbrains don't bother.