The css_xhtml head template is very similar to the xhtml head template. The only difference is that CSS that is included is specifically designed to provide the layout for the css_xhtml theme. The contents of head.ftl are:

<link rel="stylesheet" href="<@ww.url value='/webwork/css_xhtml/styles.css' encode='false' includeParams='none'/>" type="text/css"/>
<#include "/${parameters.templateDir}/simple/head.ftl" />

The contents of styles.css are:

.wwFormTable {}
.label {
    font-style:italic;
    float:left;
    width:30%
}
.errorLabel {font-style:italic; color:red; }
.errorMessage {font-weight:bold; text-align: center; color:red; }
.checkboxLabel {}
.checkboxErrorLabel {color:red; }
.required {color:red;}