当我看到网站的初始代码和示例时，CSS总是在一个单独的文件中，命名为“main.css”，“default.css”或“Site.css”。然而，当我编写一个页面时，我经常试图将CSS与DOM元素放在一起，例如在图像上设置“float: right”。我觉得这是“糟糕的编码”，因为在示例中很少这样做。
我明白，如果样式将应用于多个对象，明智的做法是遵循“不要重复自己”(Don't Repeat Yourself, DRY)，并将其分配给每个元素引用的CSS类。然而，如果我不会在另一个元素上重复CSS，为什么不内联CSS，因为我写HTML?
问题是:使用内联CSS被认为是不好的，即使它只用于该元素?如果有，为什么?
例子(这样不好吗?)
<img src="myimage.gif" style="float:right" />
当前回答
CSS的全部意义在于将内容与其表示分开。所以在你的例子中，你把内容和表现形式混在一起了，这可能是“有害的”。
其他回答
CSS的全部意义在于将内容与其表示分开。所以在你的例子中，你把内容和表现形式混在一起了，这可能是“有害的”。
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.
所以在这里我要做一个逆向的人，我要说内联css是伟大的，那些对你使用它大喊大叫的人只是在遵循他们被告知的东西，而实际上并没有给予任何原始的、公正的考虑。
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.
使用内联CSS更难维护。
对于您想要更改的每个属性，使用内联CSS要求您查找相应的HTML代码，而不是只在定义清晰且结构良好的CSS文件中查找。
除了其他答案....国际化。
根据内容语言的不同，通常需要调整元素的样式。
一个明显的例子就是从右向左的语言。
假设你使用你的代码:
<img src="myimage.gif" style="float:right" />
现在假设你想让你的网站支持rtl语言——你需要:
<img src="myimage.gif" style="float:left" />
现在，如果你想同时支持两种语言，没有办法用内联样式来赋值给float。
在CSS中，lang属性很容易解决这个问题
所以你可以这样做:
img {
float:right;
}
html[lang="he"] img { /* Hebrew. or.. lang="ar" for Arabic etc */
float:left;
}
Demo
