Revert "Revert "Fix dialog windows in place on page scroll""

This reverts commit e7bf58b.

Author: philwareham

dist/textpattern/jquery-ui.css

@@ -1156,7 +1156,7 @@ input.ui-button.ui-icon-notext .ui-icon {
 .ui-dialog {
   display: -webkit-box;
   display: flex;
-  position: absolute;
+  position: fixed;
   z-index: 1002;
   top: 0;
   left: 0;

scss/modules/_dialog.scss

@@ -35,7 +35,7 @@
 
 .ui-dialog {
     display: flex;
-    position: absolute;
+    position: fixed;
     z-index: 1002;
     top: 0;
     left: 0;