fix: insert before fixed element

integration_tests/specs/dom/nodes/insert-before.ts

@@ -129,4 +129,71 @@ describe('Insert before', () => {
     await snapshot();
   });
 
+  it('insert before position fixed element', async () => {
+    let child1 = createElement('div', {
+      style: {
+        position: 'fixed',
+        top: '100px',
+        width: '100px',
+        height: '100px',
+        background: 'red'
+      }
+    });
+    let child2;
+    const container = createElement('div', {
+      style: {
+        width: '200px',
+        height: '200px',
+        background: 'yellow'
+      }
+    }, [
+      (child2 = createElement('div', {
+        style: {
+          position: 'fixed',
+          width: '100px',
+          height: '100px',
+          background: 'green'
+        }
+      }))
+    ]);
+
+    document.body.appendChild(container);
+
+    container.insertBefore(child1, child2);
+
+    await snapshot();
+  });
+
+  it('insert before position absolute element', async () => {
+    let child1 = createElement('div', {
+      style: {
+        width: '100px',
+        height: '100px',
+        background: 'red'
+      }
+    });
+    let child2;
+    const container = createElement('div', {
+      style: {
+        width: '200px',
+        height: '200px',
+        background: 'yellow'
+      }
+    }, [
+      (child2 = createElement('div', {
+        style: {
+          position: 'absolute',
+          width: '100px',
+          height: '100px',
+          background: 'green'
+        }
+      }))
+    ]);
+
+    document.body.appendChild(container);
+
+    container.insertBefore(child1, child2);
+
+    await snapshot();
+  });
 });

kraken/lib/src/dom/element.dart

@@ -693,7 +693,17 @@ class Element extends Node
         RenderBox? afterRenderObject;
         // `referenceNode` should not be null, or `referenceIndex` can only be -1.
         if (referenceIndex != -1 && referenceNode.isRendererAttached) {
-          afterRenderObject = (referenceNode.renderer!.parentData as ContainerParentDataMixin<RenderBox>).previousSibling;
+          RenderBox renderer = referenceNode.renderer!;
+          // Renderer of referenceNode may not moved to a difference place compared to its original place
+          // in the dom tree due to position absolute/fixed.
+          // Use the renderPositionPlaceholder to get the same place as dom tree in this case.
+          if (renderer is RenderBoxModel) {
+            RenderBox? renderPositionPlaceholder = renderer.renderPositionPlaceholder;
+            if (renderPositionPlaceholder != null) {
+              renderer = renderPositionPlaceholder;
+            }
+          }
+          afterRenderObject = (renderer.parentData as ContainerParentDataMixin<RenderBox>).previousSibling;
         }
         child.attachTo(this, after: afterRenderObject);
       }