[doc] adjust the sphinx layout to match better to the dune design

cmake/scripts/conf.py.in

@@ -3,3 +3,25 @@ import sys
 sys.path.append('@DUNE_SPHINX_EXT_PATH@')
 
 extensions = ['sphinx_cmake_dune']
+
+# The theme to use for HTML and HTML Help pages.  See the documentation for
+# a list of builtin themes.
+#
+html_theme = "classic"
+html_theme_options = {
+    "rightsidebar": "true",
+    "relbarbgcolor": "#eeeeee",
+    "relbartextcolor": "#353B44",
+    "relbarlinkcolor": "#353B44",
+    "headbgcolor": "white",
+    "headtextcolor": "#353B44",
+    "linkcolor": "#337AB7",
+    "visitedlinkcolor": "#337AB7",
+    "textcolor": "#353B44",
+    "footerbgcolor": "white",
+    "footertextcolor": "#353B44",
+    "codebgcolor": "#eeeeee",
+}
+
+html_sidebars = {'**': []}
+html_title = ""