Customizing page styles for BIRT Studio
To customize BIRT Studio pages, use the files in <context root>\iportal
\bizRD\styles. This directory includes the following customizable CSS files:

accordion.css defines styles for the report design area of the page, which displays the Available Data, Report Template Items, and other selectable tree views.

dialog.css defines styles for dialog boxes that have shared characteristics, including the dialog boxes for template selection, file browsing, calculations, parameters, and so on.

dialogbase.css defines the style of dialog containers, such as the button style, the Close icon style, and so on.

title.css defines styles for the title bar of BIRT Studio pages.

toolbar.css defines styles for the toolbar.

wrcontextmenu.css defines the styles for BIRT Studio context menus.
Another file in this directory, webreporting.css, is not customizable.
For more information about using cascading style sheets, access the following URL:
http://www.w3.org/Style/CSS/