Added (to full_html and reveal templates) the possbility to read a custom.css file for tweaking the final html.

IPython/nbconvert/templates/fullhtml.tpl

@@ -28,6 +28,9 b' pre {'
 }
 </style>
 
+<!-- Custom stylesheet, it must be in the same directory as the html file -->
+<link rel="stylesheet" href="custom.css">
+
 <script src="https://c328740.ssl.cf1.rackcdn.com/mathjax/latest/MathJax.js?config=TeX-AMS_HTML" type="text/javascript">
 
 </script>

IPython/nbconvert/templates/reveal.tpl

@@ -85,6 +85,10 b' div.output_prompt {'
 text-align: inherit;
 }
 </style>
+
+<!-- Custom stylesheet, it must be in the same directory as the html file -->
+<link rel="stylesheet" href="custom.css">
+
 </head>
 {% endblock header%}