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Now you can either place your chat page as the default.htm page in the data or htdocs directory which will then override all of the theme logic, or you can create severl different 'themes' and place them in new directories under the data/themes directory. Then you can use the /?theme=
The easiest way to create a theme is to copy the default theme. It's already feature rich and should be pretty easy to edit to do what you want. However, if you find another theme that you like then use that as the base.
Step One
Create a new directory with the name of the theme that you want.
Step Two
Copy all the files in the theme that you have chosen as closest to the one that you wish to create.
Step Three
Look inside the default.htm file and find the param called ssp. Then go to the /data/params directory and copy the file that's listed in that param to a new name. As an example the default theme has an ssp file called def.prm. If your new theme is called MyTheme then change the def.prm to mytheme.prm.
Step Four
Go into your new theme and open the default.prm then change the name of def.prm to mytheme.prm
Step Five
Now you can start to change your new theme by editing the default.htm file and the ssp file.
Related Notes
Param Files
Using another web server.