In your themes jquery.sceditor.css file you have
html>body>p, html>body>div {
font: 83.33%/150% "Segoe UI", "Helvetica Neue", "Liberation Sans", "Nimbus Sans L", Arial, sans-serif;
}
Which is different than what you declared in index.css ... I'm not sure that declarion is needed or not but the font size needs to be the same since most everything in the theme is defined in em units.