app/views/layouts/digest.html.erb
<html>
<head></head>
<body style="font-family: Verdana, sans-serif; font-size: 0.8em;">
<span style="font-size: 0.8em; font-style: italic;">
<%= Redmine::WikiFormatting.to_html(Setting.text_formatting, Setting.emails_header).html_safe %>
</span>
<%= yield %>
<hr style="width: 100%; height: 1px; background: #ccc; border: 0;"/>
<span style="font-size: 0.8em; font-style: italic;">
<%= Redmine::WikiFormatting.to_html(Setting.text_formatting, Setting.emails_footer).html_safe %>
</span>
</body>
</html>