diff --git a/build.py b/build.py
index 499ed343..63bb9856 100755
--- a/build.py
+++ b/build.py
@@ -113,7 +113,7 @@ def build(ctx: BuildContext):
             "sassc",
             *SASSC_OPT,
             f"{SRC_DIR}/main/gtk-3.0/gtk-Dark.scss",
-            f"{output_dir}/gtk-3.0/gtk-dark.css",
+            f"{output_dir}/gtk-3.0/gtk-Dark.css",
         ]
     )
 
@@ -131,7 +131,7 @@ def build(ctx: BuildContext):
             "sassc",
             *SASSC_OPT,
             f"{SRC_DIR}/main/gtk-4.0/gtk-Dark.scss",
-            f"{output_dir}/gtk-4.0/gtk-dark.css",
+            f"{output_dir}/gtk-4.0/gtk-Dark.css",
         ]
     )
 
@@ -149,7 +149,7 @@ def build(ctx: BuildContext):
             "sassc",
             *SASSC_OPT,
             f"{SRC_DIR}/main/gtk-4.0/gtk-Dark.scss",
-            f"{output_dir}/gtk-4.0/gtk-dark.css",
+            f"{output_dir}/gtk-4.0/gtk-Dark.css",
         ]
     )