Possible fix

Author: pksjce

src/__tests__/anchored-position.test.ts

@@ -400,9 +400,9 @@ describe('getAnchoredPosition', () => {
     const settings: Partial<PositionSettings> = {side: 'outside-bottom', align: 'start'}
     const {top, left, anchorSide} = getAnchoredPosition(float, anchor, settings)
 
-    // Should keep the requested bottom side, allowing the overlay to extend below viewport
+    // Should flip to top side to avoid rendering below viewport, even with scrollable space
     expect(anchorSide).toEqual('outside-top')
-    expect(top).toEqual(796) // anchorRect.top + anchorRect.height + anchorOffset (4)
+    expect(top).toEqual(796) // anchorRect.top - floatingRect.height - anchorOffset (4) = 950 - 150 - 4
     expect(left).toEqual(100) // anchorRect.left
   })
 })

src/anchored-position.ts

@@ -233,11 +233,11 @@ function getClippingRect(element: Element): BoxPosition {
     left: elemRect.left + borderLeft,
     width: elemRect.width - borderRight - borderLeft,
 
-    // If the clipping node is document.body, it can expand to the full height of the window
-    height: Math.max(
-      elemRect.height - borderTop - borderBottom,
-      clippingNode === document.body ? window.innerHeight : -Infinity,
-    ),
+    // If the clipping node is document.body, use the viewport height instead of body height
+    height:
+      clippingNode === document.body
+        ? window.innerHeight
+        : Math.max(elemRect.height - borderTop - borderBottom, -Infinity),
   }
 }