Add style block for navigation block.

rainfall/theme.json

@@ -105,6 +105,14 @@
 					}
 				}
 			}
+		},
+		"blocks": {
+			"core/navigation": {
+				"typography": {
+					"fontSize": "16px",
+					"textTransform": "uppercase"
+				}
+			}
 		}
 	},
 	"templateParts": [