diff --git a/.isu/issues.json b/.isu/issues.json
index 434cb19..3fbd5f4 100644
--- a/.isu/issues.json
+++ b/.isu/issues.json
@@ -1,5 +1,5 @@
 {
-  "next_id": 379,
+  "next_id": 380,
   "issues": [
     {
       "id": 1,
@@ -4634,6 +4634,19 @@
       "author": "piefev",
       "state": "open",
       "created_at": "2026-06-19T12:18:13Z"
+    },
+    {
+      "id": 379,
+      "repo": "we",
+      "title": "Bing cached Chromium parity still exceeds threshold after carousel alignment",
+      "body": "After fixing the relative-position percentage offset that pushed the Bing carousel too low, the scenario still cannot remove the xfail from isu issue 280.\\n\\nRepro:\\n```sh\\ncargo run -p we-e2e -- --scenario crates/e2e/scenarios/real-web/bing.com.we --out-dir crates/e2e/artifacts\\n```\\n\\nCurrent observed state:\\n- DOM and interaction assertions pass.\\n- The carousel now renders in the same vertical band as the routed cached-Chromium artifact.\\n- The committed Chromium goldens are still stale against the Sichuan Tea snapshot; see isu issue 305.\\n- Comparing the current we output to the cached Chromium artifacts remains far above the harness threshold: desktop differs by about 742360/1228500 px (~60.43%) and mobile by about 226237/329160 px (~68.73%) using ImageMagick with a 1.6% fuzz approximation for the e2e tolerance.\\n- Chromium's cached render shows the white IOTD/modules section below the carousel; the we DOM dump has `.modules_wrapper` but it only contains the hidden `#vs_hidden` anchor, so the module content/height is still absent.\\n\\nArtifacts:\\n- crates/e2e/artifacts/real-web/bing.com/desktop.png\\n- crates/e2e/artifacts/real-web/bing.com/desktop.scenario-cache.chromium.png\\n- crates/e2e/artifacts/real-web/bing.com/desktop.png.diff.png\\n- crates/e2e/artifacts/real-web/bing.com/mobile.png\\n- crates/e2e/artifacts/real-web/bing.com/mobile.scenario-cache.chromium.png\\n- crates/e2e/artifacts/real-web/bing.com/mobile.png.diff.png\\n- crates/e2e/artifacts/real-web/bing.com/desktop_dom.txt\\n\\nExpected: close the remaining rendering/hydration gaps against cached Chromium, then rebaseline the stale committed goldens and remove the xfail from crates/e2e/scenarios/real-web/bing.com.we.",
+      "labels": [
+        "real-web"
+      ],
+      "assigned": [],
+      "author": "piefev",
+      "state": "open",
+      "created_at": "2026-06-19T12:38:59Z"
     }
   ]
 }
diff --git a/crates/layout/src/lib.rs b/crates/layout/src/lib.rs
index 3fb595c..dcec5cb 100644
--- a/crates/layout/src/lib.rs
+++ b/crates/layout/src/lib.rs
@@ -716,6 +716,43 @@ fn resolve_relative_vertical(top: LengthOrAuto, bottom: LengthOrAuto, cb_height:
     }
 }
 
+fn has_percentage_component(value: LengthOrAuto) -> bool {
+    match value {
+        LengthOrAuto::Percentage(_) => true,
+        LengthOrAuto::Calc(_, pct) => pct != 0.0,
+        LengthOrAuto::ClampCalc { pct, .. } => pct != 0.0,
+        LengthOrAuto::Length(_) | LengthOrAuto::Auto => false,
+    }
+}
+
+fn relative_vertical_offset_has_percentage(b: &LayoutBox) -> bool {
+    let [top, _, bottom, _] = b.css_offsets;
+    if !matches!(top, LengthOrAuto::Auto) {
+        has_percentage_component(top)
+    } else {
+        has_percentage_component(bottom)
+    }
+}
+
+fn relative_child_position_cb_height(
+    definite_parent_height: Option<f32>,
+    parent_height: f32,
+    child: &LayoutBox,
+) -> f32 {
+    if let Some(height) = definite_parent_height {
+        return height;
+    }
+
+    if child.position == Position::Relative
+        && matches!(child.css_height, LengthOrAuto::Auto)
+        && relative_vertical_offset_has_percentage(child)
+    {
+        return 0.0;
+    }
+
+    parent_height
+}
+
 // ---------------------------------------------------------------------------
 // Form control intrinsic sizing
 // ---------------------------------------------------------------------------
@@ -2741,7 +2778,7 @@ fn layout_block_children(
 
         // --- Handle floated children ---
         if is_floated(&parent.children[i]) {
-            let child_position_cb_height = definite_position_cb_height.unwrap_or(viewport_height);
+            let child_position_cb_height = definite_position_cb_height.unwrap_or(0.0);
             layout_float_child(
                 &mut parent.children[i],
                 &mut float_ctx,
@@ -2807,7 +2844,7 @@ fn layout_block_children(
 
         // `compute_layout` adds `child.margin.top` internally, so compensate.
         let y_for_child = cursor_y + collapsed_top - child_top_margin;
-        let child_position_cb_height = definite_position_cb_height.unwrap_or(viewport_height);
+        let child_position_cb_height = definite_position_cb_height.unwrap_or(0.0);
         compute_layout(
             &mut parent.children[i],
             content_x,
@@ -2856,8 +2893,12 @@ fn layout_block_children(
         }
     }
 
-    let final_position_cb_height = definite_position_cb_height.unwrap_or(parent.rect.height);
     for child in &mut parent.children {
+        let final_position_cb_height = relative_child_position_cb_height(
+            definite_position_cb_height,
+            parent.rect.height,
+            child,
+        );
         apply_relative_offset(child, content_width, final_position_cb_height);
     }
 }
@@ -8112,6 +8153,47 @@ p { margin: 0; }
         assert_eq!(div_box.relative_offset, (0.0, 0.0));
     }
 
+    #[test]
+    fn relative_top_percentage_in_auto_height_parent_uses_zero_reference() {
+        let mut doc = Document::new();
+        let (_, _, body) = make_html_body(&mut doc);
+        let parent = doc.create_element("div");
+        let child = doc.create_element("div");
+        let inner = doc.create_element("div");
+        let sibling = doc.create_element("div");
+        doc.append_child(body, parent);
+        doc.append_child(parent, child);
+        doc.append_child(child, inner);
+        doc.append_child(parent, sibling);
+        doc.set_attribute(body, "style", "margin:0;");
+        doc.set_attribute(parent, "style", "position:relative;width:400px;");
+        doc.set_attribute(child, "style", "position:relative;top:calc(100% - 47px);");
+        doc.set_attribute(inner, "style", "height:100px;");
+        doc.set_attribute(sibling, "style", "height:50px;");
+
+        let tree = layout_doc(&doc);
+        let parent_box = find_box(&tree.root, parent).unwrap();
+        let child_box = find_box(&tree.root, child).unwrap();
+        let sibling_box = find_box(&tree.root, sibling).unwrap();
+
+        assert!(
+            (parent_box.rect.height - 150.0).abs() < 0.01,
+            "parent should keep its normal-flow auto height, got {}",
+            parent_box.rect.height
+        );
+        assert_eq!(child_box.relative_offset, (0.0, -47.0));
+        assert!(
+            (child_box.rect.y - (parent_box.rect.y - 47.0)).abs() < 0.01,
+            "child y should use zero as the percentage reference, got {}",
+            child_box.rect.y
+        );
+        assert!(
+            (sibling_box.rect.y - (parent_box.rect.y + 100.0)).abs() < 0.01,
+            "relative offset must not affect sibling normal flow, got {}",
+            sibling_box.rect.y
+        );
+    }
+
     #[test]
     fn relative_position_bottom_right() {
         // bottom: 15px should shift up by 15px (negative direction).
@@ -10279,6 +10361,59 @@ body { margin: 0; }
         );
     }
 
+    #[test]
+    fn relative_top_percentage_inside_static_wrapper_abspos_uses_stretched_height() {
+        let mut doc = Document::new();
+        let (_, _, body) = make_html_body(&mut doc);
+        let wrapper = doc.create_element("div");
+        let abs_child = doc.create_element("div");
+        let rel_child = doc.create_element("div");
+        let tile = doc.create_element("div");
+        doc.append_child(body, wrapper);
+        doc.append_child(wrapper, abs_child);
+        doc.append_child(abs_child, rel_child);
+        doc.append_child(rel_child, tile);
+        doc.set_attribute(body, "style", "margin:0;");
+        doc.set_attribute(wrapper, "style", "height:100%;");
+        doc.set_attribute(
+            abs_child,
+            "style",
+            "position:absolute;top:calc(5vh + 9.0625rem);bottom:0;left:0;right:0;",
+        );
+        doc.set_attribute(
+            rel_child,
+            "style",
+            "position:relative;top:calc(100% - 12.6875rem);height:100px;",
+        );
+        doc.set_attribute(tile, "style", "height:50px;");
+
+        let font = test_font();
+        let sheets = extract_stylesheets(&doc);
+        let styled = resolve_styles(&doc, &sheets, (1365.0, 900.0)).unwrap();
+        let tree = layout(&styled, &doc, 1365.0, 900.0, &font, &HashMap::new());
+        let abs_box = find_box(&tree.root, abs_child).unwrap();
+        let rel_box = find_box(&tree.root, rel_child).unwrap();
+
+        let expected_abs_y = 45.0 + 145.0;
+        let expected_abs_height = 900.0 - expected_abs_y;
+        let expected_rel_y = expected_abs_y + expected_abs_height - 203.0;
+        assert!(
+            (abs_box.rect.y - expected_abs_y).abs() < 0.01,
+            "absolute y should be {expected_abs_y}, got {}",
+            abs_box.rect.y
+        );
+        assert!(
+            (abs_box.rect.height - expected_abs_height).abs() < 0.01,
+            "absolute child should stretch to {expected_abs_height}, got {}",
+            abs_box.rect.height
+        );
+        assert!(
+            (rel_box.rect.y - expected_rel_y).abs() < 0.01,
+            "relative child y should be {expected_rel_y}, got {}",
+            rel_box.rect.y
+        );
+    }
+
     #[test]
     fn nested_flex_row_items_do_not_overlap() {
         // Regression for isu issue 327: a flex row that is itself a flex item