Add world settings command and related files

src/shared-ui/world-background-style.ts

@@ -0,0 +1,17 @@
+import type { CSSProperties } from "react";
+
+import type { WorldBackgroundSettings } from "../document/world-settings";
+
+export function createWorldBackgroundStyle(background: WorldBackgroundSettings): CSSProperties {
+  if (background.mode === "solid") {
+    return {
+      backgroundColor: background.colorHex,
+      backgroundImage: "none"
+    };
+  }
+
+  return {
+    backgroundColor: background.bottomColorHex,
+    backgroundImage: `linear-gradient(180deg, ${background.topColorHex} 0%, ${background.bottomColorHex} 100%)`
+  };
+}