add close button for setup overlay

frontend/style.css

@@ -260,6 +260,13 @@ body {
     max-width: 500px;
     width: 90%;
     border: 1px solid var(--border);
+    position: relative;
+}
+
+#closeSetupButton {
+    position: absolute;
+    top: 1rem;
+    right: 1.5rem;
 }
 
 .setup-card h2 {