Set htmlTemplate
to something like the following
# Can be used to add default HTML code (e.g. default header section with CSS).
htmlTemplate = """
<html>
<head>
<link rel="stylesheet" type="text/css" charset="utf-8" media="screen" href="http://paste.ubuntu.com/static/pastebin.css">
</head>
<body>
%s
</body>
</html>
"""