fix(safari): handle scrollingElement=body correctly (#256)

* fix positioning calculation in safari

* also fix older safari versions

Author: stipsan

src/compute.ts

@@ -243,10 +243,10 @@ export default (
   // https://www.quirksmode.org/blog/archives/2016/02/chrome_change_b.html
   const viewportWidth = window.visualViewport
     ? window.visualViewport.width
-    : viewport.clientWidth
+    : Math.min(viewport.clientWidth, window.innerWidth)
   const viewportHeight = window.visualViewport
     ? window.visualViewport.height
-    : viewport.clientHeight
+    : Math.min(viewport.clientHeight, window.innerHeight)
   const viewportX = window.scrollX || window.pageXOffset
   const viewportY = window.scrollY || window.pageYOffset
 
@@ -316,7 +316,7 @@ export default (
         targetBlock = targetRect.top + targetRect.height / 2
       }
       if (viewport === frame) {
-        blockScroll = viewportY + targetBlock - frame.clientHeight / 2
+        blockScroll = viewportY + targetBlock - viewportHeight / 2
       } else {
         // prevent negative scrollTop values
         const offset =
@@ -335,7 +335,7 @@ export default (
         targetBlock = targetRect.bottom
       }
       if (viewport === frame) {
-        blockScroll = viewportY + targetBlock - frame.clientHeight
+        blockScroll = viewportY + targetBlock - viewportHeight
       } else {
         // prevent negative scrollTop values
         const offset =
@@ -399,7 +399,7 @@ export default (
         targetInline = targetRect.left + targetRect.width / 2
       }
       if (viewport === frame) {
-        inlineScroll = viewportX + targetInline - frame.clientWidth / 2
+        inlineScroll = viewportX + targetInline - viewportWidth / 2
       } else {
         // prevent negative scrollLeft values
         const offset =
@@ -418,7 +418,7 @@ export default (
         targetInline = targetRect.right
       }
       if (viewport === frame) {
-        inlineScroll = viewportX + targetInline - frame.clientWidth
+        inlineScroll = viewportX + targetInline - viewportWidth
       } else {
         // prevent negative scrollLeft values
         const offset =