Test

tests/test_style_properties.py

@@ -0,0 +1,9 @@
+from textual.color import Color
+from textual.css.styles import Styles
+
+
+def test_box_normalization():
+    """Check that none or hidden is normalized to empty string."""
+    styles = Styles()
+    styles.border_left = ("none", "red")
+    assert styles.border_left == ("", Color.parse("red"))