Using Preview toolbar

Preview toolbar allows to customize internal preview.

To show or hide the toolbar, on the View menu, click Preview Toolbar.

Preview toolbar commands

Preview File box specifies the file or address to be used to generate preview.
Open Preview File allows to add preview file. This command is used to select HTML file to preview Style Sheet on.
Refresh Preview reloads internal preview. This is useful when the file has changed after the preview was generated.
Show Rulers shows or hides internal preview rulers. Rulers are useful for determining element widths and heights in web pages.
Close Preview closes the preview pane and enters full window text editing mode. Does the same as clicking Code Editor tab at the bottom of document window.