fix correct font-family not applying for multiple select element

themes/light/prefs.less

@@ -9,6 +9,10 @@ body.ttrss_prefs {
 		color : @default-text;
 	}
 
+	select[multiple="multiple"] option {
+		font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
+	}
+
 	.text-muted {
 		color : @fg-text-muted;
 	}

themes/light/tt-rss.less

@@ -9,6 +9,10 @@ body.ttrss_main {
 		outline: none;
 	}
 
+	select[multiple="multiple"] option {
+		font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
+	}
+
 	.post {
 		padding : 0;
 		font-size : @font-size-toolbar;