diff --git a/py/hexagram/svg.py b/py/hexagram/svg.py
index 6df81d4..91a5902 100644
--- a/py/hexagram/svg.py
+++ b/py/hexagram/svg.py
@@ -1,11 +1,13 @@
 import cairo
 import gi
 
+from typing import Optional
+
 gi.require_version('Rsvg', '2.0')
 
 from gi.repository import Rsvg
 
-def to_surface(path: str, width: float, height: float, style: str) -> cairo.Surface:
+def to_surface(path: str, width: float, height: float, style: Optional[str]=None) -> cairo.Surface:
     surface = cairo.RecordingSurface(cairo.CONTENT_ALPHA,
                                      cairo.Rectangle(0, 0, width, height))
 
@@ -18,7 +20,10 @@ def to_surface(path: str, width: float, height: float, style: str) -> cairo.Surf
     rect.height = height
 
     svg = Rsvg.Handle.new_from_file(path)
-    svg.set_stylesheet(bytes(style, 'utf8'))
+
+    if style is not None:
+        svg.set_stylesheet(bytes(style, 'utf8'))
+
     svg.render_layer(cr, None, rect)
 
     return surface