--- a/libervia/server/pages.py	Tue May 19 11:05:47 2020 +0200
+++ b/libervia/server/pages.py	Tue May 19 11:05:50 2020 +0200
@@ -1345,6 +1345,7 @@
 
         return self.host.renderer.render(
             self.template,
+            theme=session_data.theme,
             site_themes=self.vhost_root.site_themes,
             page_url=self.getURL(),
             media_path=f"/{C.MEDIA_DIR}",
@@ -1666,6 +1667,24 @@
             if session_data.locale is None:
                 self.setBestLocale(request)
 
+            # theme
+            key_theme = C.KEY_THEME.encode()
+            if key_theme in request.args:
+                try:
+                    theme = request.args.pop(key_theme)[0].decode()
+                except IndexError:
+                    theme = C.TEMPLATE_THEME_DEFAULT
+                else:
+                    if key_theme != session_data.theme:
+                        if theme not in self.vhost_root.site_themes:
+                            log.warning(_(
+                                "Theme {theme!r} doesn't exist for {vhost}, using "
+                                "default one")
+                                .format(theme=theme, vhost=self.vhost_root))
+                        else:
+                            session_data.theme = theme
+
+
         d = defer.Deferred()
         d.addCallback(self._checkAccess, request)