What's the difference between inline styles vs classes?

Question

In my head, I've always known to use classes over inline styles for any project. But are there any effective differences between the two?

Solution 1

There is a simple reason. The point of CSS is to separate the content (HTML) from the presentation (CSS). It's all about accessibility and code reuse.

Solution 2

First of all:

• If the HTML is built or generated independent of the overall site design (e.g. shared template code), then add reasonably-named classes and IDs, linked exclusively to external stylesheet(s). Use sufficient elements to allow for arbitrary CSS manipulation. For example, see the CSS Zen Garden. This applies to ALL CMSes, programs, scripts, and other dynamically-generated site content. The HTML output must contain absolutely no styling or layout of any sort at all. No exceptions.

Assuming you're dealing with static content, then:

• If there's any way you can reuse the style, make it a class and link to a stylesheet.

• If there's no way would ever reuse the style (it's a one-off thing that doesn't make sense anywhere else) then use a <style> block that references the element's #id.

• If the CSS attribute only makes sense in the context of the surrounding HTML (e.g. some usages of clear:) then I inline the style into the element.

A lot of people call this heresy, just like a lot of people denounce any use of goto in modern programming languages.

However, rather than subscribing to stylistic dogma, my view is you should chose the method based on your circumstances that decreases your overall workload the most. Stylesheets add a level of indirection that makes site-level changes easy and helps build consistency. But if you have several dozen classes on each page that are only used in one place, then you're actually increasing your workload, not decreasing it.

In other words, don't do something dumb and confusing just because people tell you it's the right way to do it.

Solution 3

If the choice was there, my first preference will be classes/other selectors. However, there are situations where inline styles are the only way to go. In other situations, just a CSS class by itself requires too much work, and other types of CSS selectors make more sense there.

Suppose you had to zebra stripe a given list or table. Instead of applying a particular class to each alternate element or row, you could simply use selectors to do the job. That will keep the code simple, but it won't be using CSS classes. To illustrate the three ways:

Using only class

.alternate {
    background-color: #CCC;
}

<ul>
    <li>first</li>
    <li class="alternate">second</li>
    <li>third</li>
    <li class="alternate">fourth</li>
</ul>

Using class + structural selectors

.striped :nth-child(2n) {
    background-color: #CCC;
}

<ul class="striped">
    <li>first</li>
    <li>second</li>
    <li>third</li>
    <li>fourth</li>
</ul>

Using inline styles

<ul>
    <li>first</li>
    <li style="background-color: #CCC">second</li>
    <li>third</li>
    <li style="background-color: #CCC">fourth</li>
</ul>

The second way looks the most portable and encapsulated to me. To add or remove stripes from any given container element, simply add or remove the striped class.

However, there are cases where inline styles not only make sense, but are the only way to go. When the set of possible values is huge, it will be stupid to try to make classes in advance for each possible state. For example, a UI that allows the user to dynamically place certain items anywhere on the screen by dragging. The item will have to be positioned absolutely or relatively with actual coordinates such as:

<div style="position: absolute; top: 20px; left: 49px;">..</div>

Surely, we could use classes for each possible position the div can take, but that's not recommended. And one can easily see why:

.pos_20_49 {
    top: 20px;
    left: 49px;
}
.pos_20_50 {
    top: 20px;
    left: 50px;
}
// keep going for a million such classes if the container size is 1000x1000 px

<div class="pos_20_49">..</div>

Solution 4

Use common sense.

Everyone knows that presentation and content should, in an ideal world, be separated. Everyone also knows that this doesn't work very well a lot of the time. We all know that you're supposed to use divs rather than tables for layout, but we also know that for any circumstance where you don't have full control over the content it just doesn't work properly.

Downloading a 500k style sheet to style one element because you've taken every possible style and stuck it in a style sheet will kill your page, downloading 500 smaller style sheets to style your page because you need them all will also kill your page.

Reuse is great in concept, but the reality is that it's only useful in certain contexts. This applies equally to pretty much anywhere the concept exists. If your project does what you want it to do, does so in every reasonable browser, does so in an efficient way, and does so reliably, then you're good to go, it's not dramatically harder to refactor css than is is code.

Solution 5

I can't think of any pros for inline styles.

CSS is all about Progressive Enhancement, and not repeating yourself (DRY).

With stylesheets, Changing the look becomes as easy as changing one line in the HTML code. Make a mistake or the client doesn't like the change? revert to the old stylesheet.

Other advantages:

1. Your site can automagically adjust to different media, such as for printout and for hand-held devices.

2. Conditionally-included CSS fixes, for that gawd-awful browser-that-shall-not-be-named, become a snap.

3. Your users can easily customize the site with plugins like Stylish.

4. You can more easily reuse or share code from site to site.

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Comments

[stinky472]

+1 it all comes down to reuse. But sometimes inlining a style which has little or no potential for reuse can help reduce clutter in the library of classes that are actually worth reusing.

[Chuck]

Was that meant to be "changing one line in the CSS code"? Because changing one line in HTML could change the look even if you weren't separating content from presentation.

[Justin Johnson]

On the other hand, markup can be cached as well; however, caching CSS is easier since CSS is more likely to be static than HTML. Just saying.

[Brock Adams]

@Chuck: No that was one line in the HTML. Changing from OldCSS_File.css to NewCSS_File.css, for example.

[qwerty123]

@Justin: Fair point. My intent wasn't to imply that pages could not be or were not cached; my apologies if that is how it was received. My point was that CSS is typically a fairly static resource and separation buys you an effective and simple means of caching. With the dynamic nature of many pages, the options for content caching often require more planning and sophistication. However, it is fair to say that is dependant upon the complexity of the content on a given site and for static content the CSS cache benefit that I mentioned is moot as the entire page can easily be cached.

[Justin Johnson]

I wasn't disagreeing with you ;) just pointing out that HTML can be cached as well.

[Steve Wortham]

Then there's the speed/size advantages. An external CSS file can define redundant formatting rules, sometimes drastically cutting down the size of your HTML. And an external CSS file can be downloaded once and cached for the duration of the user's visit.

[Sukhpreet Singh Alang]

@Brock Adams, A pro of inline styles is definitely there with modularized applications. When modules are independent, they do not know what classes exist. Thus, they have to create their own.

[Dirk Boer]

I mainly agree to these points, but if you take it a point further: why not ditch the style block and ids (point #3) - and instead just use inline for these elements? First of all this means you don't have to add useless id's to tags that don't need them anyway, and you decrease your workload by not having to jump around in the document. Besides that I don't see what it really adds anyway :)

[JoshNaro]

I think point #3 may be speculating that it's possible/probable that you create or run into another spot where the style may be used in the future and can swap out the ID for a class at that time. I've had this happen a good bit in the past.

[Ivan Rave]

@DirkBoer, some styles can't be inlined: stackoverflow.com/questions/1033156/…

[Dirk Boer]

@IvanRave, agreed. It's not a static rule, I'm just in favor of pragmatism :)