Initialize League GUI prototype

src/components/ui/Modal.tsx

@@ -0,0 +1,29 @@
+import type { ReactNode } from "react";
+import { Button } from "./Button";
+
+type ModalProps = {
+  open: boolean;
+  title: string;
+  children: ReactNode;
+  onClose: () => void;
+};
+
+export function Modal({ open, title, children, onClose }: ModalProps) {
+  if (!open) {
+    return null;
+  }
+
+  return (
+    <div className="ui-modal-backdrop" role="presentation">
+      <section className="ui-modal" role="dialog" aria-modal="true" aria-labelledby="modal-title">
+        <header className="ui-modal-header">
+          <h2 id="modal-title">{title}</h2>
+          <Button variant="ghost" size="sm" onClick={onClose} aria-label="Close modal">
+            Close
+          </Button>
+        </header>
+        <div>{children}</div>
+      </section>
+    </div>
+  );
+}