Are you using the toolbar to style things, or dragging things on the page? If so, EW is creating the styles you are asking it to. To avoid that, create your own styles and apply them, don't use the toolbar for styling, and don't drag things across
the page or resize things on the page. When you create your own styles, you have a choice to put them in an external CSS page or in the page header section. Pick the one you want.