update default font size for presentation

template.html

@@ -4,6 +4,9 @@
 <title>My Slideshow</title>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
 <style type="text/css">
+  body{
+  font-size: 2em;
+  }
   .remark-code {
   border-radius: 6px;
   }