AC-112: Modal z-index error when deleting item from cart

- Fixed z-index calculation using jQuery UI implementation
- Fixed styling

Author: Rrego6

app/code/Magento/Ui/view/base/web/js/modal/modal.js

@@ -24,7 +24,7 @@ define([
      * Detect browser transition end event.
      * @return {String|undefined} - transition event.
      */
-    var transitionEvent =  (function () {
+    var transitionEvent = (function () {
         var transition,
             elementStyle = document.createElement('div').style,
             transitions = {
@@ -39,7 +39,39 @@ define([
                 return transitions[transition];
             }
         }
-    })();
+    })(),
+
+    /**
+     * Implementation of zIndex used from jQuery UI
+     * @param {Element} elem
+     * @private
+     */
+    getZIndex = function (elem) {
+        var position, zIndex;
+
+        /* eslint-disable max-depth */
+        while (elem.length && elem[ 0 ] !== document) {
+            // Ignore z-index if position is set to a value where z-index is ignored by the browser
+            // This makes behavior of this function consistent across browsers
+            // WebKit always returns auto if the element is positioned
+            position = elem.css('position');
+
+            if (position === 'absolute' || position === 'relative' || position === 'fixed') {
+                // IE returns 0 when zIndex is not specified
+                // other browsers return a string
+                // we ignore the case of nested elements with an explicit value of 0
+                zIndex = parseInt(elem.css('zIndex'), 10);
+
+                if (!isNaN(zIndex) && zIndex !== 0) {
+                    return zIndex;
+                }
+            }
+            elem = elem.parent();
+        }
+
+        return 0;
+        /* eslint-enable max-depth */
+    };
 
     /**
      * Modal Window Widget
@@ -341,18 +373,17 @@ define([
          * Set z-index and margin for modal and overlay.
          */
         _setActive: function () {
-            var zIndex = this.modal.zIndex(),
+            var zIndex = getZIndex(this.modal),
                 baseIndex = zIndex + this._getVisibleCount();
 
             if (this.modal.data('active')) {
                 return;
             }
-
             this.modal.data('active', true);
 
-            this.overlay.zIndex(++baseIndex);
-            this.prevOverlayIndex = this.overlay.zIndex();
-            this.modal.zIndex(this.overlay.zIndex() + 1);
+            this.overlay.css('z-index', ++baseIndex);
+            this.prevOverlayIndex = baseIndex;
+            this.modal.css('z-index', baseIndex + 1);
 
             if (this._getVisibleSlideCount()) {
                 this.modal.css('marginLeft', this.options.modalLeftMargin * this._getVisibleSlideCount());
@@ -367,7 +398,7 @@ define([
             this.modal.data('active', false);
 
             if (this.overlay) {
-                this.overlay.zIndex(this.prevOverlayIndex - 1);
+                this.overlay.css('z-index', this.prevOverlayIndex - 1);
             }
         },