From 9fb37084c94885fa677f28c3d7259a99b544bf36 Mon Sep 17 00:00:00 2001
From: Justin Kahn <justindavidkahn@gmail.com>
Date: Fri, 21 Jun 2019 17:51:04 +0800
Subject: [PATCH 1/2] fix(Overlay): wrapper position absolute-close #812

---
 src/overlay/main.scss | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/overlay/main.scss b/src/overlay/main.scss
index 03d243f226..17c1309419 100644
--- a/src/overlay/main.scss
+++ b/src/overlay/main.scss
@@ -1,6 +1,10 @@
 @import "../core/index-noreset.scss";
 
 .#{$css-prefix}overlay-wrapper {
+    position: absolute;
+    top: 0;
+    left: 0;
+
     .#{$css-prefix}overlay-inner {
         z-index: 1001;
     }

From 52ddf8da21935162e4e2985e5c0085be039420b9 Mon Sep 17 00:00:00 2001
From: Justin Kahn <justindavidkahn@gmail.com>
Date: Mon, 24 Jun 2019 11:54:57 +0800
Subject: [PATCH 2/2] fix(Overlay): comment out unnecessary code

---
 src/overlay/utils/position.js | 48 ++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 21 deletions(-)

diff --git a/src/overlay/utils/position.js b/src/overlay/utils/position.js
index db8c3df7c3..a10d54684c 100644
--- a/src/overlay/utils/position.js
+++ b/src/overlay/utils/position.js
@@ -191,27 +191,33 @@ export default class Position {
     }
 
     _makeElementInViewport(pinElement, number, type, isPinFixed) {
-        let result = number;
-        const docElement = document.documentElement;
-        const offsetParent =
-            pinElement.offsetParent || document.documentElement;
-
-        if (result < 0) {
-            if (isPinFixed) {
-                result = 0;
-            } else if (
-                offsetParent === document.body &&
-                dom.getStyle(offsetParent, 'position') === 'static'
-            ) {
-                // Only when div's offsetParent is document.body, we set new position result.
-                result = Math.max(
-                    docElement[`scroll${type}`],
-                    document.body[`scroll${type}`]
-                );
-            }
-        }
-
-        return result;
+        // pinElement.offsetParent is never body because wrapper has position: absolute
+        // refactored to make code clearer. Revert if wrapper style changes.
+
+        // let result = number;
+        // const docElement = document.documentElement;
+        // const offsetParent =
+        //     pinElement.offsetParent || document.documentElement;
+
+        // if (result < 0) {
+        //     if (isPinFixed) {
+        //         result = 0;
+        //     }
+
+        //     else if (
+        //         offsetParent === document.body &&
+        //         dom.getStyle(offsetParent, 'position') === 'static'
+        //     ) {
+        //         // Only when div's offsetParent is document.body, we set new position result.
+        //         result = Math.max(
+        //             docElement[`scroll${type}`],
+        //             document.body[`scroll${type}`]
+        //         );
+        //     }
+        // }
+        // return result;
+
+        return number < 0 && isPinFixed ? 0 : number;
     }
 
     _normalizePosition(element, align, isPinFixed) {