add more functions

app.py

@@ -260,8 +260,20 @@ def annotate_cyclic_structure(mol, sequence):
     # Convert to PIL Image
     img = Image.open(BytesIO(drawer.GetDrawingText()))
     draw = ImageDraw.Draw(img)
-    font = ImageFont.load_default(60)
-    small_font = ImageFont.load_default(60)
+    try:
+        # Try to use DejaVuSans as it's commonly available on Linux systems
+        font = ImageFont.truetype("/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf", 60)
+        small_font = ImageFont.truetype("/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf", 60)
+    except OSError:
+        try:
+            # Fallback to Arial if available (common on Windows)
+            font = ImageFont.truetype("arial.ttf", 60)
+            small_font = ImageFont.truetype("arial.ttf", 60)
+        except OSError:
+            # If no TrueType fonts are available, fall back to default
+            print("Warning: TrueType fonts not available, using default font")
+            font = ImageFont.load_default()
+            small_font = ImageFont.load_default()
 
     # Get molecule bounds
     conf = mol.GetConformer()