You can find this section under Interface & Design > Trade CSS Stylesheet in the IRP left navigation menu.
You use this section to define the entire stylesheet for your Trade (B2B) website, as held on the file system. Any changes you make here will be immediately reflected on the trade site. You can also edit the Live Support Style Sheet using this page — the stylesheet contains all the style information used by the Live Support feature.
This section works essentially in the same way as the IRP Retail setup — for details see the following help topics:
If you make any changes, click the Update Trade Stylesheet button. You can see what effect your changes will have by clicking the Preview button.