The xhtml head template extends the simple head template and provides an additional CSS that helps render the xhtml theme form elements. The contents of head.ftl are:

<link rel="stylesheet" href="<@ww.url value='/webwork/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; }
.errorLabel {font-style:italic; color:red; }
.errorMessage {font-weight:bold; text-align: center; color:red; }
.checkboxLabel {}
.checkboxErrorLabel {color:red; }
.required {color:red;}
.tdLabel { text-align:right; vertical-align:top; }