They have the same effect on normal web browser rendering engines, but there is a fundamental difference between them. As the author writes in a discussion list post: Think of three different. Em has the purpose of giving em phasis to the content. I heard you should define sizes and distances in your stylesheet with em instead of in pixels. So the question is why should i use em instead of px when defining styles in css? Both of them emphasize text. Tag shows text as italics, whereas <strong> Is this the only difference? 即为此表情，代码为 [em]e3006 [/em] 1、当发送或接收出现问题时，表情可能显示为代码。 2、此表情适用范围仅限于 qq空间 中的留言板，聊天窗口无法显示。 3、此表情显示的画面是一个.

The 'em' is a very useful unit in css, since it can adapt automatically to the font that the reader uses an em is relative to the current element it is defined on. If you use relative.

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