fix(pat-bumper): Do not calculate padding/margin on viewport.

On the viewport as scrolling container paddings and margins are not
influencing the sticky element's position. This is contrary to other
scrolling containers within the document. The position calculation is
easier and only consists of the clientWidth/Height to respect scrollbar
widths.

Author: thet

src/pat/bumper/bumper.js

@@ -33,23 +33,11 @@ class Pattern extends BasePattern {
 
         // Viewport dimensions
         this.dim_viewport = {
-            top:
-                0 +
-                dom.get_css_value(document.body, "margin-top", true) +
-                dom.get_css_value(document.body, "padding-top", true),
-            left:
-                0 +
-                dom.get_css_value(document.body, "margin-left", true) +
-                dom.get_css_value(document.body, "padding-left", true),
+            top: 0,
+            right: document.documentElement.clientWidth,
+            bottom: document.documentElement.clientHeight,
+            left: 0,
         };
-        this.dim_viewport.right =
-            document.documentElement.clientWidth -
-            dom.get_css_value(document.body, "margin-right", true) -
-            dom.get_css_value(document.body, "padding-right", true);
-        this.dim_viewport.bottom =
-            document.documentElement.clientHeight -
-            dom.get_css_value(document.body, "margin-bottom", true) -
-            dom.get_css_value(document.body, "padding-bottom", true);
 
         this.dim_element = {
             top: dom.get_css_value(this.el, "top", true),