How do I differentiate .content in right-sidebar and left-sidebar

Generally each region has an outer div with a unique id, something like <div id="left-sidebar">...</div>. You can then use that id to apply different styling to .content like this

Get yourself Firebug (http://www.getfirebug.com). It will help you to identify all the div id's and classes used.

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Joep
CompuBase, Drupal websites and design