diff --git a/.epub/example/OEBPS/scripts/ipub.js b/.epub/example/OEBPS/scripts/ipub.js
index 1a9e3e2..f70a681 100644
--- a/.epub/example/OEBPS/scripts/ipub.js
+++ b/.epub/example/OEBPS/scripts/ipub.js
@@ -28,49 +28,84 @@ class IPUBBackground extends IPUBElement {
   /**
    * @private
    */
-  static #observer = (() => {
-    /** @type {Map<string, IPUBBackground>} */
-    const instancesOnScreen = new Map();
-
-    document.addEventListener("scroll", () => {
-      for (const [_, instance] of instancesOnScreen) {
-        const perc = getPercentageInView(
-          instance.querySelector("img") || instance,
+  static #instancesOnScreen = {
+    /** @type {Map<IPUBBody, Set<IPUBBackground>>} */
+    map: new Map(),
+    /**
+     * @param {IPUBBackground} background
+     */
+    add(background) {
+      const body = getAncestor(background, IPUBBody.elementName);
+      if (!body) {
+        console.error(
+          `IPUBBackground: ${background.id} does not have a valid ipub-body ancestor`,
         );
-        instance.fade(perc);
+        return;
       }
-    });
 
-    return new IntersectionObserver((entries) =>
-      entries.forEach((e) => {
-        let instance = e.target.parentElement;
+      let set = this.map.get(body);
+      if (!set) {
+        set = new Set();
+        body.addEventListener("scroll", () => {
+          for (const instance of set.values()) {
+            const perc = getPercentageInView(
+              instance.querySelector("img") || instance,
+            );
+            instance.fade(perc);
+          }
+        });
+      }
+      set.add(background);
+      this.map.set(body, set);
+    },
+    /**
+     * @param {IPUBBackground} background
+     */
+    remove(background) {
+      const body = getAncestor(background, IPUBBody.elementName);
+      if (!body) {
+        console.error(
+          `IPUBBackground: ${background.id} does not have a valid ipub-body ancestor`,
+        );
+        return;
+      }
 
-        if (
-          instance.tagName.toLowerCase() !==
-          IPUBBackground.elementName.toLowerCase()
-        ) {
-          instance = instance.parentElement;
-        }
+      const set = this.map.get(body);
+      if (!set) {
+        return;
+      }
 
-        if (
-          instance.tagName.toLowerCase() !==
-          IPUBBackground.elementName.toLowerCase()
-        ) {
-          console.error(
-            "IPUBBackground: malformed <ipub-background> element",
-            e.target,
-          );
-          return;
-        }
+      set.delete(background);
 
-        if (e.intersectionRatio > 0 && instance.id) {
-          instancesOnScreen.set(instance.id, instance);
-        } else if (instance.id) {
-          instancesOnScreen.delete(instance.id);
-        }
-      }),
-    );
-  })();
+      if (set.size === 0) {
+        this.map.delete(body);
+      }
+    },
+  };
+  static addToScreen() {}
+
+  /**
+   * @private
+   */
+  static #observer = new IntersectionObserver((entries) => {
+    for (const { intersectionRatio, target: image } of entries) {
+      const instance = getAncestor(image, IPUBBackground.elementName);
+
+      if (!instance) {
+        console.error(
+          "IPUBBackground: malformed <ipub-background> element",
+          image,
+        );
+        return;
+      }
+
+      if (intersectionRatio > 0 && instance.id) {
+        IPUBBackground.#instancesOnScreen.add(instance);
+      } else if (instance.id) {
+        IPUBBackground.#instancesOnScreen.remove(instance);
+      }
+    }
+  });
 
   connectedCallback() {
     super.connectedCallback();
@@ -126,8 +161,6 @@ class IPUBBackground extends IPUBElement {
    * @returns {void | Promise<void>}
    */
   fade(perc) {
-    console.debug(`IPUBBackground: ${this.id} is ${perc} on screen`);
-
     if (!this.style.getPropertyValue("--ipub-fade")) {
       this.style.setProperty("--ipub-fade", `${perc}%`);
       return;
@@ -264,7 +297,19 @@ class IPUBInteraction extends IPUBElement {
     }
 
 /**
+ * @param {HTMLElement} el
+ * @param {string} tagName
+ * @returns {HTMLElement | undefined}
  */
+function getAncestor(el, tagName) {
+  if (!el.parentElement) {
+    return undefined;
+  }
+  if (el.parentElement.tagName.toLowerCase() === tagName.toLowerCase()) {
+    return el.parentElement;
+  }
+  return getAncestor(el.parentElement, tagName);
+}
 
 /**
  * @param {Readonly<Element>} el
@@ -330,3 +375,4 @@ function getPercentageInView(element) {
 
   return Math.round((inView / globalThis.innerHeight) * 100);
 }
+