Add a default font style (#2755)

examples/select2/index.html

@@ -8,6 +8,9 @@
     <link href="http://cdnjs.cloudflare.com/ajax/libs/select2/4.0.0/css/select2.min.css" rel="stylesheet">
     <script src="http://cdnjs.cloudflare.com/ajax/libs/select2/4.0.0/js/select2.min.js"></script>
     <style>
+      html, body {
+        font: 13px/18px sans-serif;
+      }
       select {
         min-width: 300px;
       }