In the Ant scripts used to build the DITA Open Toolkit User Guide and Reference, we initially used only the default CSS stylesheet. However, the default CSS for XHTML does not have a filepath class defined, so all <filepath> elements are unstyled. For this reason we have added a custom CSS file that styles .filepath using the Courier font family. Here is what the CSS file looks like:
/* Stylesheet overrides for DITA Open Toolkit Users Guide and Reference */
/* DITAOT_UGRef_CSS.css */
.filepath { font-family: courier }