Use the same fonts as github for code in Helios. They look rather good

on all platforms I tried.

css/helios.css

@@ -16,7 +16,7 @@ html[xmlns] .clearfix {
   height: 1%;
 }
 .cm-s-helios.CodeMirror {
-  font-family: Menlo, Monaco, Consolas, Inconsolata, "Lucida Console", Courier, monospace;
+  font-family: Consolas, "Liberation Mono", Courier, monospace;
   line-height: 16px;
   font-size: 13px;
 }

css/helios.less

@@ -21,7 +21,7 @@ html[xmlns] .clearfix {
 
 .cm-s-helios {
 	&.CodeMirror {
-		font-family: Menlo, Monaco, Consolas, Inconsolata, "Lucida Console", Courier, monospace;
+		font-family: Consolas, "Liberation Mono", Courier, monospace;
 		line-height: 16px;
 		font-size: 13px;
 	}