Want to test this in PSP

types/index.d.ts

@@ -51,6 +51,7 @@
 /// <reference path="./save/save.d.ts" />
 
 // ui
+/// <reference path="./ui/fullbox.d.ts" />
 /// <reference path="./ui/textbox.d.ts" />
 
 // engine systems

types/ui/fullbox.d.ts

@@ -0,0 +1,39 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+/** A full-screen color overlay. */
+interface UIFullboxInstance {
+  /**
+   * Sets the overlay to a solid color with no animation.
+   * Returns a Promise that resolves immediately.
+   * @param color - The color to apply.
+   */
+  setColor(color: Color): Promise<void>;
+
+  /**
+   * Animates the overlay from one color to another.
+   * Returns a Promise that resolves when the transition completes.
+   * Starting a new transition while one is in progress resolves the
+   * old Promise immediately before beginning the new one.
+   * @param from     - Starting color.
+   * @param to       - Ending color.
+   * @param duration - Duration in seconds.
+   * @param easing   - Optional EASING_* constant (default: EASING_LINEAR).
+   */
+  transition(
+    from: Color,
+    to: Color,
+    duration: number,
+    easing?: number
+  ): Promise<void>;
+}
+
+/** Full-screen overlay drawn on top of all UI elements. */
+declare var UIFullboxOver: UIFullboxInstance;
+
+/** Full-screen overlay drawn below all UI elements. */
+declare var UIFullboxUnder: UIFullboxInstance;