diff --git a/voila/configuration.py b/voila/configuration.py
index 33ff57150..0de8891f6 100644
--- a/voila/configuration.py
+++ b/voila/configuration.py
@@ -7,7 +7,7 @@
 #############################################################################
 
 import traitlets.config
-from traitlets import Unicode, Bool
+from traitlets import Unicode, Bool, Dict
 
 
 class VoilaConfiguration(traitlets.config.Configurable):
@@ -20,34 +20,13 @@ class VoilaConfiguration(traitlets.config.Configurable):
             'template name to be used by voila.'
         )
     )
-    reveal_theme = Unicode(
-        'simple',
+    extra_resources = Dict(
+        {},
         allow_none=True,
         help="""
-        Used only with template reveal, ignored otherwise.
-        Name of the reveal.js theme to use.
-        We look for a file with this name under
-        ``reveal_url_prefix``/css/theme/``reveal_theme``.css.
-        https://github.com/hakimel/reveal.js/tree/master/css/theme has
-        list of themes that ship by default with reveal.js.
-        """
-    ).tag(config=True)
-    reveal_transition = Unicode(
-        'slide',
-        allow_none=True,
-        help="""
-        Used only with template reveal, ignored otherwise.
-        Name of the reveal.js transition to use.
-        The list of transitions that ships by default with reveal.js are:
-        none, fade, slide, convex, concave and zoom.
-        """
-    ).tag(config=True)
-    reveal_scroll = Bool(
-        False,
-        allow_none=True,
-        help="""
-        Used only with template reveal, ignored otherwise.
-        If True, enable scrolling within each slide
+        extra resources used by templates;
+        example use with --template=reveal
+        --extra_resources="{'reveal': {'transition': 'fade', 'scroll': True}}"
         """
     ).tag(config=True)
     theme = Unicode('light').tag(config=True)
diff --git a/voila/handler.py b/voila/handler.py
index a347fd986..031832dca 100644
--- a/voila/handler.py
+++ b/voila/handler.py
@@ -72,13 +72,29 @@ def get(self, path=None):
         # add extra resources (necessary for reveal template)
         resources_reveal = {
             'reveal': {
-                'theme': self.voila_configuration.reveal_theme,
-                'transition': self.voila_configuration.reveal_transition,
-                'scroll': self.voila_configuration.reveal_scroll,
+                'theme': 'simple',
+                'transition': 'slide',
+                'scroll': False,
             }
         }
         resources.update(resources_reveal)
 
+        # include potential extra resources
+        extra_resources = self.voila_configuration.extra_resources
+        if extra_resources:
+            for k in extra_resources.keys():
+                if k in resources.keys():
+                    if isinstance(extra_resources[k], dict):
+                        for kk in extra_resources[k].keys():
+                            # update or add depth-2 resources
+                            resources[k][kk] = extra_resources[k][kk]
+                        else:
+                            # update depth-1 (top-level) resources
+                            resources[k] = extra_resources[k]
+                else:
+                    # add depth-1 (top-level) resources
+                    resources[k] = extra_resources[k]
+
         exporter = VoilaExporter(
             template_path=self.nbconvert_template_paths,
             config=self.exporter_config,