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Forum Themes
The ExpressionEngine forums make use of "themes" to determine how they are displayed. The Forum Module comes with a "default" theme, which is located in your installation under themes/forum_themes/.
The theme files may be edited from within the ExpressionEngine Control Panel under Modules > Discussion Forum > Templates. In order for you to be able to edit the Templates inside the Control Panel, you must first set the theme .php files to 666 permissions (for Windows servers, you need to make them "writable").
If you plan to make changes to your theme, we recommend that you make a copy of the themes/forum_themes/default/ directory, name it something else, and make your changes to that one. You can assign the theme for your forum to use under the Default Preferences.
If you have more than one theme installed, you can easily change between your themes simply by choosing a new one under Default Preferences.
For anyone creating their own theme or modifying one, the original "PSD" version of the "ExpressionEngine Forums" graphic is available for download.