+2  A: 

Each email client handles CSS differently. Gmail is notorious for its lack of CSS support. To get it consistent across all clients/webapps you will probably have to use tables with inline styles.

This link is helpful: http://www.campaignmonitor.com/css/

cmoylan  2010-09-14 03:46:35
[This article](http://www.groundwire.org/support/articles/css-and-email-newsletters) is also helpful for explaining why this might be happening - as chris say's do the CSS inline and don't style the body tag as it is often ignored too :)
stephenmurdoch  2010-09-14 03:51:40
also, chris's tip about using tables is good advice
stephenmurdoch  2010-09-14 03:53:50

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