1.5 theme upgrade
From MoodleDocs
How To Upgrade Your Theme from Moodle 1.4 to 1.5
In Moodle 1.5 a lot of work has been done to extend the CSS support to all parts of Moodle and to remove any old hardcoded styles (such as fonts or colors) from the HTML code. As a result Moodle themes are a lot more flexible and accessible, but this also means that custom themes written for Moodle 1.4 and earlier no longer work very well.
This documents covers the steps needed for converting your old Moodle 1.4 theme to Moodle 1.5. It's also useful even if you are starting from scratch with a new Moodle 1.5 theme.