diff --git a/colormaestro/formatters/css.py b/colormaestro/formatters/css.py
index 9ad8999..6334347 100644
--- a/colormaestro/formatters/css.py
+++ b/colormaestro/formatters/css.py
@@ -11,6 +11,9 @@ def generate(palette):
     Returns:
         str: CSS variables definition
     """
+    if not palette:
+        return ":root {\n}\n"
+
     css = ":root {\n"
 
     # Add color variables
diff --git a/tests/test_generators.py b/tests/test_generators.py
index 6339288..d0a716b 100644
--- a/tests/test_generators.py
+++ b/tests/test_generators.py
@@ -188,7 +188,7 @@ def test_basic_generation(self):
     def test_dark_mode(self):
         """Test dark mode UI palette generation"""
         base_color = SAMPLE_COLORS['blue']
-        palette = ui_palette.generate(base_color, 5, dark=True)
+        palette = ui_palette.generate(base_color, 5, dark_mode=True)
 
         # Check that the palette has the correct length
         assert len(palette) == 5