This is to keep the CSS validator happy.

themes/css/sans-08.css

@@ -1,5 +1,5 @@
 body, td, th, dd, dt, h1, h2, h3, h4, h5, h6, p, ol, ul, li {
-  font-family: helvetica,arial,sans;
+  font-family: helvetica,arial,sans-serif;
 }
 body {
   font-size: 6pt;

themes/css/sans-10.css

@@ -1,5 +1,5 @@
 body, td, th, dd, dt, h1, h2, h3, h4, h5, h6, p, ol, ul, li {
-  font-family: helvetica,arial,sans;
+  font-family: helvetica,arial,sans-serif;
 }
 body {
   font-size: 8pt;

themes/css/sans-12.css

@@ -1,5 +1,5 @@
 body, td, th, dd, dt, h1, h2, h3, h4, h5, h6, p, ol, ul, li {
-  font-family: helvetica,arial,sans;
+  font-family: helvetica,arial,sans-serif;
 }
 body {
   font-size: 10pt;