From e7e5e67baf8f0d1b7e040e4351366add44034a6a Mon Sep 17 00:00:00 2001
From: Sebastian Markbage <sebastian@calyptus.eu>
Date: Mon, 29 Sep 2025 15:14:17 -0400
Subject: [PATCH] Use the scrollWidth/Height for the root when the root is the
 documentElement

---
 .../src/backend/fiber/renderer.js               | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/packages/react-devtools-shared/src/backend/fiber/renderer.js b/packages/react-devtools-shared/src/backend/fiber/renderer.js
index 0dd3084af5a..cde4a589494 100644
--- a/packages/react-devtools-shared/src/backend/fiber/renderer.js
+++ b/packages/react-devtools-shared/src/backend/fiber/renderer.js
@@ -2251,8 +2251,23 @@ export function attach(
     }
     if (typeof instance.getClientRects === 'function') {
       // DOM
-      const result: Array<Rect> = [];
       const doc = instance.ownerDocument;
+      if (instance === doc.documentElement) {
+        // This is the document element. The size of this element is not actually
+        // what determines the whole scrollable area of the screen. Because any
+        // thing that overflows the document will also contribute to the scrollable.
+        // This is unlike overflow: scroll which clips those.
+        // Therefore, we use the scrollable size for this rect instead.
+        return [
+          {
+            x: 0,
+            y: 0,
+            width: instance.scrollWidth,
+            height: instance.scrollHeight,
+          },
+        ];
+      }
+      const result: Array<Rect> = [];
       const win = doc && doc.defaultView;
       const scrollX = win ? win.scrollX : 0;
       const scrollY = win ? win.scrollY : 0;