diff --git a/apps/viewer-demo/scripts/verify-pptx-slideshow.mjs b/apps/viewer-demo/scripts/verify-pptx-slideshow.mjs
index fded59a86..f9e6bbd13 100644
--- a/apps/viewer-demo/scripts/verify-pptx-slideshow.mjs
+++ b/apps/viewer-demo/scripts/verify-pptx-slideshow.mjs
@@ -287,9 +287,15 @@ await page.waitForFunction(
   { timeout: 5_000 }
 )
 assert.equal(await call('overlayCount'), 1, 'shadow viewer should be presenting')
+await page.waitForFunction(
+  () => window.__slideshowTest.presentationIsVisible('shadow'),
+  null,
+  { timeout: 5_000 }
+)
+assert.equal(await call('presentationIsVisible', 'shadow'), true, 'shadow viewer should show its active slide')
 await call('exitFullscreen')
 await waitOverlay(0, 5_000)
-console.log('13) shadow-root native fullscreen exit closes the overlay')
+console.log('13) shadow-root fullscreen shows the slide and browser exit closes the overlay')
 
 // 14) Enter/Space on the focused exit button activates it, not the slide.
 await call('enter', 'default')
diff --git a/apps/viewer-demo/src/slideshow-test.ts b/apps/viewer-demo/src/slideshow-test.ts
index 0f58cab33..60b2972f1 100644
--- a/apps/viewer-demo/src/slideshow-test.ts
+++ b/apps/viewer-demo/src/slideshow-test.ts
@@ -12,6 +12,7 @@ interface SlideshowTestApi {
   presenting: (name: ViewerName) => boolean
   activeNumber: (name: ViewerName) => number
   activeSlideHasContent: (name: ViewerName) => boolean
+  presentationIsVisible: (name: ViewerName) => boolean
   counter: (name: ViewerName) => string
   transform: (name: ViewerName) => string
   overlayCount: () => number
@@ -177,6 +178,39 @@ const init = async () => {
         : active
       return Boolean(slide && slide.classList.contains('slide') && slide.textContent?.trim())
     },
+    presentationIsVisible: name => {
+      const overlay = overlayFor(name) as HTMLElement | null
+      const viewer = viewers.get(name)
+      if (!overlay || !viewer) {
+        return false
+      }
+      const containers = Array.from(
+        viewer.content.querySelectorAll<HTMLElement>(':scope > .flyfish-pptx-slide-slot, :scope > .slide')
+      )
+      const active = containers.find(container => container.classList.contains('is-active-slide'))
+      const slide = active?.classList.contains('flyfish-pptx-slide-slot')
+        ? active.firstElementChild as HTMLElement | null
+        : active
+      if (!slide) {
+        return false
+      }
+      const root = overlay.getRootNode()
+      const hasViewerStyles = root instanceof ShadowRoot
+        ? Boolean(root.querySelector('#flyfish-pptx-native-style'))
+        : Boolean(document.getElementById('flyfish-pptx-native-style'))
+      const overlayRect = overlay.getBoundingClientRect()
+      const slideRect = slide.getBoundingClientRect()
+      const slideStyle = getComputedStyle(slide)
+      const intersectsOverlay = slideRect.right > overlayRect.left &&
+        slideRect.left < overlayRect.right &&
+        slideRect.bottom > overlayRect.top &&
+        slideRect.top < overlayRect.bottom
+      return hasViewerStyles &&
+        slideStyle.display !== 'none' &&
+        slideRect.width > 0 &&
+        slideRect.height > 0 &&
+        intersectsOverlay
+    },
     counter: name => overlayFor(name)?.querySelector('.flyfish-pptx-presentation-counter')?.textContent ?? '',
     transform: name => viewers.get(name)?.content.style.transform ?? '',
     overlayCount: () => deepAll('.flyfish-pptx-presentation').length,
diff --git a/packages/renderers/pptx/src/viewer.ts b/packages/renderers/pptx/src/viewer.ts
index 978e1c6e6..95e9be6f4 100644
--- a/packages/renderers/pptx/src/viewer.ts
+++ b/packages/renderers/pptx/src/viewer.ts
@@ -238,19 +238,27 @@ export class PptxViewer {
     return this.presentation?.slideNumber ?? 1;
   }
 
+  private get styleRoot(): Document | ShadowRoot {
+    if (this.options.styleRoot) {
+      return this.options.styleRoot;
+    }
+    const documentRef = this.target.ownerDocument || document;
+    const root = this.target.getRootNode();
+    const ShadowRootCtor = documentRef.defaultView?.ShadowRoot;
+    return ShadowRootCtor && root instanceof ShadowRootCtor
+      ? root as ShadowRoot
+      : documentRef;
+  }
+
   /**
    * Where the slideshow overlay is mounted. It has to share a root with the injected slide styles,
    * or the engine's scoped CSS stops applying once the slides move into the overlay.
    */
   get presentationRoot(): ShadowRoot | HTMLElement {
     const documentRef = this.target.ownerDocument || document;
-    if (this.options.styleRoot) {
-      return this.options.styleRoot;
-    }
-    const root = this.target.getRootNode();
-    const ShadowRootCtor = documentRef.defaultView?.ShadowRoot;
-    if (ShadowRootCtor && root instanceof ShadowRootCtor) {
-      return root as ShadowRoot;
+    const styleRoot = this.styleRoot;
+    if (styleRoot !== documentRef) {
+      return styleRoot as ShadowRoot;
     }
     return documentRef.body || documentRef.documentElement;
   }
@@ -325,7 +333,7 @@ export class PptxViewer {
 
   async open() {
     ensureZipWithinLimits(this.buffer, this.options);
-    ensurePptxViewerStyles(this.target.ownerDocument || document, this.options.styleRoot);
+    ensurePptxViewerStyles(this.target.ownerDocument || document, this.styleRoot);
     this.target.replaceChildren(this.scaleBox);
     this.attachResizeObserver();
     this.attachSlideWindowListeners();