diff --git a/src/npe2/manifest/_bases.py b/src/npe2/manifest/_bases.py
index 630b75bf..d5e7d7c7 100644
--- a/src/npe2/manifest/_bases.py
+++ b/src/npe2/manifest/_bases.py
@@ -78,7 +78,7 @@ def from_file(cls, path: Union[Path, str]):
             try:
                 import tomllib
             except ImportError:
-                import tomli as tomllib  # type: ignore [no-redef]
+                import tomli as tomllib
 
             loader = tomllib.load
         elif path.suffix.lower() in (".yaml", ".yml"):
diff --git a/src/npe2/manifest/contributions/_themes.py b/src/npe2/manifest/contributions/_themes.py
index fa9e2bb3..8085c2b3 100644
--- a/src/npe2/manifest/contributions/_themes.py
+++ b/src/npe2/manifest/contributions/_themes.py
@@ -1,3 +1,4 @@
+import sys
 from typing import Literal, Optional, Union
 
 from pydantic import BaseModel, color
@@ -65,5 +66,6 @@ class ThemeContribution(BaseModel):
         '   - HSL strings: "`hsl(270, 60%, 70%)"`, `"hsl(270, 60%, 70%, .5)`"\n'
     )
     font_size: str = Field(
-        description="Font size (in points, pt) used in the application."
+        default="12pt" if sys.platform == "darwin" else "9pt",
+        description="Font size (in points, pt) used in the application.",
     )