Also, this from Microsoft's Prerequisites for Using Microsoft Expression Web:
Is Expression Web a What-You-See-Is-What-You-Get (WYSIWYG) tool?
No. Expression Web does a good job of approximating what your page will look like in any particular browser. However, the Expression Web design surface does not fully support all code that you might be using. For example, CSS pseudo-element styles are not rendered in Design view in Expression Web.
When you want to see exactly how a particular page will look in a browser, you should preview that page in the desired browser. Expression Web contains a robust feature-set for previewing in multiple browsers at the desired screen resolution..
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