When exporting a report to HTML format, a .css file will be generated automatically by JReport to control the appearance and layout of the result file. When exporting a report to HTML format with Server API, JReport enables you to apply your own .css file to the HTML result file.
To apply user defined CSS to HTML result file:
Select the object which you want to apply in your own CSS, and in Report Inspector, specify a value for the CSS property External CSS Class Selector. The value of the property should be the selector in your .css file.
<install_root>\help\server\en\samples for your reference.