added code from unity

Runtime/UI/PopupReference.cs

@@ -0,0 +1,23 @@
+using UnityEngine;
+
+namespace Jovian.PopupSystem.UI {
+    /// <summary>
+    /// Reference-only MonoBehaviour for a popup prefab. Holds serialized scene references
+    /// to the content container, canvas group, and background. All behavior is in
+    /// <see cref="PopupView"/>.
+    /// </summary>
+    public class PopupReference : MonoBehaviour {
+        [SerializeField] RectTransform content;
+        [SerializeField] CanvasGroup canvasGroup;
+        [SerializeField] RectTransform background;
+
+        /// <summary>The content RectTransform where popup elements are parented.</summary>
+        public RectTransform Content => content;
+
+        /// <summary>The CanvasGroup for fade animation control.</summary>
+        public CanvasGroup CanvasGroup => canvasGroup;
+
+        /// <summary>The background RectTransform that sizes to content.</summary>
+        public RectTransform Background => background;
+    }
+}