This is the anwser of IBM to a very similar question:
I have my own style sheets that I want to use for my reports. How do I
make them available from Report Assistant?
In Report Assistant, on the Reporting options tab, you can specify a style sheet under the
Apply an existing WebFocus Stylesheet field. To add your own style sheets to this list:
1. Copy your stylesheet files to the integrated file system directory
After they are in that directory, they are available to every domain for importing.
2. To import, open the desired domain, right-click the Other Files folder, and select Import.
3. In the Select Files to Add dialog window that opens, from the list of style sheets, select the
stylesheet files and click Save.
The style sheets are now available from Report Assistant.
Tip: Many sample style sheets are provided as part of the base product and can be
used in your reports. They have the file extension .STY and can be found in the
integrated file system directory \QIBM\UserData\webquery\ibi\webfocus76\template.
To make these style sheets available in the Report Assistant interface, copy the .STY
files to the directory specified in step 1 above and follow the remaining steps.
Attention: Although custom style sheets should work in DB2 Web Query, IBM Support
does not provide assistance if you should experience problems.
I hope this help you