The generic CSS font family name is 'sans-serif', not 'sans'

css/amber.css

@@ -241,7 +241,7 @@ body.amberBody {
 .amberTool textarea,
 .amberTool input {
     border: 0 none;
-    font-family:  "DejaVu Sans", Helvetica, sans;
+    font-family:  "DejaVu Sans", Helvetica, sans-serif;
     line-height: 1.3em;
     font-size: 11px;
     position: relative;
@@ -250,7 +250,7 @@ body.amberBody {
 
 .amberTool .CodeMirror {
     border: 0 none;
-    font-family:  "DejaVu Sans", Helvetica, sans;
+    font-family:  "DejaVu Sans", Helvetica, sans-serif;
     font-size: 11px;
     line-height: 1.3em;
     height: 100%;
@@ -262,7 +262,7 @@ body.amberBody {
 }
 
 .amberTool .CodeMirror-scroll pre {
-    font-family: "DejaVu Sans", Helvetica, sans;
+    font-family: "DejaVu Sans", Helvetica, sans-serif;
 }
 
 .amberTool .amber_clear {

css/helios.css

@@ -34,7 +34,7 @@ html[xmlns] .clearfix {
 }
 body[id="helios"] {
   font-size: 11px;
-  font-family: "Lucida Grande", "Segoe UI", helvetica, arial, sans;
+  font-family: "Lucida Grande", "Segoe UI", helvetica, arial, sans-serif;
   background: #eee;
 }
 body[id="helios"] a {
@@ -54,7 +54,7 @@ body[id="helios"] .CodeMirror {
 }
 body[id="helios"] .CodeMirror-hints {
   border-radius: 0;
-  font-family: "Lucida Grande", "Segoe UI", helvetica, arial, sans;
+  font-family: "Lucida Grande", "Segoe UI", helvetica, arial, sans-serif;
   font-size: 11px;
   line-height: 1em;
   padding: 0;

css/helios.less

@@ -44,7 +44,7 @@ html[xmlns] .clearfix {
 
 body[id="helios"] {
 	font-size: 11px;
-	font-family: "Lucida Grande", "Segoe UI", helvetica, arial, sans;
+	font-family: "Lucida Grande", "Segoe UI", helvetica, arial, sans-serif;
 	background: #eee;
 
 	a {
@@ -67,7 +67,7 @@ body[id="helios"] {
 
 	.CodeMirror-hints {
 		border-radius: 0;
-		font-family: "Lucida Grande", "Segoe UI", helvetica, arial, sans;
+		font-family: "Lucida Grande", "Segoe UI", helvetica, arial, sans-serif;
 		font-size: 11px;
 		line-height: 1em;
 		padding: 0;