What's so bad about in-line CSS?

Question

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

1. Easy to maintain your html page
2. Change to the Look and feel will be easy and you can have support for many themes on your pages.
3. 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