Initial attempt @ submenu implementation.

src/components/dropdownMenu/DropdownMenuSubContent.tsx

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+import * as DropdownMenuPrimitive from "@radix-ui/react-dropdown-menu";
+import { useDevice } from "../App";
+import Stack from "../Stack";
+import { Island } from "../Island";
+import clsx from "clsx";
+
+const DropdownMenuSubContent = ({
+  children,
+  className,
+}: {
+  children?: React.ReactNode;
+  className?: string;
+}) => {
+  const device = useDevice();
+
+  const classNames = clsx(`dropdown-menu ${className}`, {
+    "dropdown-menu--mobile": device.isMobile,
+  }).trim();
+
+  return (
+    <DropdownMenuPrimitive.SubContent className={classNames}>
+      {device.isMobile ? (
+        <Stack.Col className="dropdown-menu-container">{children}</Stack.Col>
+      ) : (
+        <Island
+          className="dropdown-menu-container"
+          padding={2}
+          style={{ zIndex: 1 }}
+        >
+          {children}
+        </Island>
+      )}
+    </DropdownMenuPrimitive.SubContent>
+  );
+};
+
+export default DropdownMenuSubContent;
+DropdownMenuSubContent.displayName = "DropdownMenuSubContent";