diff --git a/incorporealcms/config.py b/incorporealcms/config.py
index 5ed4258..f5bd28a 100644
--- a/incorporealcms/config.py
+++ b/incorporealcms/config.py
@@ -50,6 +50,12 @@ class Config(object):
     MEDIA_DIR = 'media'
 
     # customizations
+    PAGE_STYLES = {
+        'dark': 'css/dark.css',
+        'light': 'css/light.css',
+        'plain': 'css/plain.css',
+    }
+
     DEFAULT_PAGE_STYLE = 'light'
     TITLE_SUFFIX = 'example.com'
     CONTACT_EMAIL = 'admin@example.com'
diff --git a/incorporealcms/lib.py b/incorporealcms/lib.py
index 5973e1f..6bf8cd8 100644
--- a/incorporealcms/lib.py
+++ b/incorporealcms/lib.py
@@ -31,19 +31,14 @@ def render(template_name_or_list, **context):
 
     * Determine the proper site theme to use in the template and provide it.
     """
-    PAGE_STYLES = {
-        'dark': 'css/dark.css',
-        'light': 'css/light.css',
-        'plain': 'css/plain.css',
-    }
-
+    page_styles = app.config['PAGE_STYLES']
     selected_style = request.args.get('style', None)
     if selected_style:
         user_style = selected_style
     else:
         user_style = request.cookies.get('user-style')
         logger.debug("user style cookie: %s", user_style)
-    context['user_style'] = PAGE_STYLES.get(user_style, PAGE_STYLES.get(app.config['DEFAULT_PAGE_STYLE']))
+    context['user_style'] = page_styles.get(user_style, page_styles.get(app.config['DEFAULT_PAGE_STYLE']))
 
     resp = make_response(render_template(template_name_or_list, **context))
     if selected_style:
diff --git a/tests/test_pages.py b/tests/test_pages.py
index 244abe0..9a1b0e6 100644
--- a/tests/test_pages.py
+++ b/tests/test_pages.py
@@ -1,10 +1,15 @@
 """Unit test helper methods."""
+import os
+
 import pytest
 from werkzeug.http import dump_cookie
 
+from incorporealcms import create_app
 from incorporealcms.pages import (generate_parent_navs, instance_resource_path_to_request_path, render,
                                   request_path_to_breadcrumb_display, request_path_to_instance_resource_path)
 
+HERE = os.path.dirname(os.path.abspath(__file__))
+
 
 def test_generate_page_navs_index(app):
     """Test that the index page has navs to the root (itself)."""
@@ -67,6 +72,29 @@ def test_render_with_no_user_theme(app):
         assert b'/static/css/dark.css' not in render('base.html').data
 
 
+def test_render_with_theme_overrides(app):
+    """Test that the loaded themes can be overridden from the default."""
+    cookie = dump_cookie("user-style", 'cool')
+    restyled_app = create_app(instance_path=os.path.join(HERE, 'instance'),
+                              test_config={'PAGE_STYLES': {'cool': 'css/cool.css',
+                                                           'warm': 'css/warm.css'}})
+    with restyled_app.test_request_context(headers={'COOKIE': cookie}):
+        assert b'/static/css/cool.css' in render('base.html').data
+        assert b'/static/css/warm.css' not in render('base.html').data
+
+
+def test_render_with_theme_overrides_not_found_is_default(app):
+    """Test that theme overrides work, and if a requested theme doesn't exist, the default is loaded."""
+    cookie = dump_cookie("user-style", 'nonexistent')
+    restyled_app = create_app(instance_path=os.path.join(HERE, 'instance'),
+                              test_config={'PAGE_STYLES': {'cool': 'css/cool.css',
+                                                           'warm': 'css/warm.css'},
+                                           'DEFAULT_PAGE_STYLE': 'warm'})
+    with restyled_app.test_request_context(headers={'COOKIE': cookie}):
+        assert b'/static/css/warm.css' in render('base.html').data
+        assert b'/static/css/nonexistent.css' not in render('base.html').data
+
+
 def test_request_path_to_instance_resource_path(app):
     """Test a normal URL request is transformed into the file path."""
     with app.test_request_context():