Update calculation of element offsets (#1739)

* Update element offset computation

Updated logic for computing element top and left offset to use document.documentElement and window, from document.body since document.body always returns 0

Signed-off-by: AngeloKarugo <52207274+AngeloKarugo@users.noreply.github.com>

* made new element offset calculation method, changed scrollspy offset method

---------

Signed-off-by: AngeloKarugo <52207274+AngeloKarugo@users.noreply.github.com>

src/js/dom/manipulator.js

@@ -151,6 +151,27 @@ const Manipulator = {
   hasClass(element, className) {
     return element.classList.contains(className);
   },
+
+  maxOffset(element) {
+    const rect = element.getBoundingClientRect();
+
+    return {
+      top:
+        rect.top +
+        Math.max(
+          document.body.scrollTop,
+          document.documentElement.scrollTop,
+          window.scrollY
+        ),
+      left:
+        rect.left +
+        Math.max(
+          document.body.scrollLeft,
+          document.documentElement.scrollLeft,
+          window.scrollX
+        ),
+    };
+  },
 };
 
 function _classNameOrListToArray(classNameOrList) {

src/js/navigation/scrollspy.js

@@ -67,7 +67,7 @@ const SELECTOR_LINK_ITEMS = `${SELECTOR_NAV_LINKS}, ${SELECTOR_LIST_ITEMS}, ${SE
 const SELECTOR_DROPDOWN = "[data-te-dropdown-ref]";
 const SELECTOR_DROPDOWN_TOGGLE = "[data-te-dropdown-toggle-ref]";
 
-const METHOD_OFFSET = "offset";
+const METHOD_OFFSET = "maxOffset";
 const METHOD_POSITION = "position";
 
 /*