diff --git a/wp-includes/js/dist/vendor/wp-polyfill-inert.js b/wp-includes/js/dist/vendor/wp-polyfill-inert.js
new file mode 100644
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--- /dev/null
+++ b/wp-includes/js/dist/vendor/wp-polyfill-inert.js
@@ -0,0 +1,840 @@
+(function (global, factory) {
+  typeof exports === 'object' && typeof module !== 'undefined' ? factory() :
+  typeof define === 'function' && define.amd ? define('inert', factory) :
+  (factory());
+}(this, (function () { 'use strict';
+
+  var _createClass = function () { function defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } } return function (Constructor, protoProps, staticProps) { if (protoProps) defineProperties(Constructor.prototype, protoProps); if (staticProps) defineProperties(Constructor, staticProps); return Constructor; }; }();
+
+  function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }
+
+  /**
+   * This work is licensed under the W3C Software and Document License
+   * (http://www.w3.org/Consortium/Legal/2015/copyright-software-and-document).
+   */
+
+  (function () {
+    // Return early if we're not running inside of the browser.
+    if (typeof window === 'undefined') {
+      return;
+    }
+
+    // Convenience function for converting NodeLists.
+    /** @type {typeof Array.prototype.slice} */
+    var slice = Array.prototype.slice;
+
+    /**
+     * IE has a non-standard name for "matches".
+     * @type {typeof Element.prototype.matches}
+     */
+    var matches = Element.prototype.matches || Element.prototype.msMatchesSelector;
+
+    /** @type {string} */
+    var _focusableElementsString = ['a[href]', 'area[href]', 'input:not([disabled])', 'select:not([disabled])', 'textarea:not([disabled])', 'button:not([disabled])', 'details', 'summary', 'iframe', 'object', 'embed', '[contenteditable]'].join(',');
+
+    /**
+     * `InertRoot` manages a single inert subtree, i.e. a DOM subtree whose root element has an `inert`
+     * attribute.
+     *
+     * Its main functions are:
+     *
+     * - to create and maintain a set of managed `InertNode`s, including when mutations occur in the
+     *   subtree. The `makeSubtreeUnfocusable()` method handles collecting `InertNode`s via registering
+     *   each focusable node in the subtree with the singleton `InertManager` which manages all known
+     *   focusable nodes within inert subtrees. `InertManager` ensures that a single `InertNode`
+     *   instance exists for each focusable node which has at least one inert root as an ancestor.
+     *
+     * - to notify all managed `InertNode`s when this subtree stops being inert (i.e. when the `inert`
+     *   attribute is removed from the root node). This is handled in the destructor, which calls the
+     *   `deregister` method on `InertManager` for each managed inert node.
+     */
+
+    var InertRoot = function () {
+      /**
+       * @param {!HTMLElement} rootElement The HTMLElement at the root of the inert subtree.
+       * @param {!InertManager} inertManager The global singleton InertManager object.
+       */
+      function InertRoot(rootElement, inertManager) {
+        _classCallCheck(this, InertRoot);
+
+        /** @type {!InertManager} */
+        this._inertManager = inertManager;
+
+        /** @type {!HTMLElement} */
+        this._rootElement = rootElement;
+
+        /**
+         * @type {!Set<!InertNode>}
+         * All managed focusable nodes in this InertRoot's subtree.
+         */
+        this._managedNodes = new Set();
+
+        // Make the subtree hidden from assistive technology
+        if (this._rootElement.hasAttribute('aria-hidden')) {
+          /** @type {?string} */
+          this._savedAriaHidden = this._rootElement.getAttribute('aria-hidden');
+        } else {
+          this._savedAriaHidden = null;
+        }
+        this._rootElement.setAttribute('aria-hidden', 'true');
+
+        // Make all focusable elements in the subtree unfocusable and add them to _managedNodes
+        this._makeSubtreeUnfocusable(this._rootElement);
+
+        // Watch for:
+        // - any additions in the subtree: make them unfocusable too
+        // - any removals from the subtree: remove them from this inert root's managed nodes
+        // - attribute changes: if `tabindex` is added, or removed from an intrinsically focusable
+        //   element, make that node a managed node.
+        this._observer = new MutationObserver(this._onMutation.bind(this));
+        this._observer.observe(this._rootElement, { attributes: true, childList: true, subtree: true });
+      }
+
+      /**
+       * Call this whenever this object is about to become obsolete.  This unwinds all of the state
+       * stored in this object and updates the state of all of the managed nodes.
+       */
+
+
+      _createClass(InertRoot, [{
+        key: 'destructor',
+        value: function destructor() {
+          this._observer.disconnect();
+
+          if (this._rootElement) {
+            if (this._savedAriaHidden !== null) {
+              this._rootElement.setAttribute('aria-hidden', this._savedAriaHidden);
+            } else {
+              this._rootElement.removeAttribute('aria-hidden');
+            }
+          }
+
+          this._managedNodes.forEach(function (inertNode) {
+            this._unmanageNode(inertNode.node);
+          }, this);
+
+          // Note we cast the nulls to the ANY type here because:
+          // 1) We want the class properties to be declared as non-null, or else we
+          //    need even more casts throughout this code. All bets are off if an
+          //    instance has been destroyed and a method is called.
+          // 2) We don't want to cast "this", because we want type-aware optimizations
+          //    to know which properties we're setting.
+          this._observer = /** @type {?} */null;
+          this._rootElement = /** @type {?} */null;
+          this._managedNodes = /** @type {?} */null;
+          this._inertManager = /** @type {?} */null;
+        }
+
+        /**
+         * @return {!Set<!InertNode>} A copy of this InertRoot's managed nodes set.
+         */
+
+      }, {
+        key: '_makeSubtreeUnfocusable',
+
+
+        /**
+         * @param {!Node} startNode
+         */
+        value: function _makeSubtreeUnfocusable(startNode) {
+          var _this2 = this;
+
+          composedTreeWalk(startNode, function (node) {
+            return _this2._visitNode(node);
+          });
+
+          var activeElement = document.activeElement;
+
+          if (!document.body.contains(startNode)) {
+            // startNode may be in shadow DOM, so find its nearest shadowRoot to get the activeElement.
+            var node = startNode;
+            /** @type {!ShadowRoot|undefined} */
+            var root = undefined;
+            while (node) {
+              if (node.nodeType === Node.DOCUMENT_FRAGMENT_NODE) {
+                root = /** @type {!ShadowRoot} */node;
+                break;
+              }
+              node = node.parentNode;
+            }
+            if (root) {
+              activeElement = root.activeElement;
+            }
+          }
+          if (startNode.contains(activeElement)) {
+            activeElement.blur();
+            // In IE11, if an element is already focused, and then set to tabindex=-1
+            // calling blur() will not actually move the focus.
+            // To work around this we call focus() on the body instead.
+            if (activeElement === document.activeElement) {
+              document.body.focus();
+            }
+          }
+        }
+
+        /**
+         * @param {!Node} node
+         */
+
+      }, {
+        key: '_visitNode',
+        value: function _visitNode(node) {
+          if (node.nodeType !== Node.ELEMENT_NODE) {
+            return;
+          }
+          var element = /** @type {!HTMLElement} */node;
+
+          // If a descendant inert root becomes un-inert, its descendants will still be inert because of
+          // this inert root, so all of its managed nodes need to be adopted by this InertRoot.
+          if (element !== this._rootElement && element.hasAttribute('inert')) {
+            this._adoptInertRoot(element);
+          }
+
+          if (matches.call(element, _focusableElementsString) || element.hasAttribute('tabindex')) {
+            this._manageNode(element);
+          }
+        }
+
+        /**
+         * Register the given node with this InertRoot and with InertManager.
+         * @param {!Node} node
+         */
+
+      }, {
+        key: '_manageNode',
+        value: function _manageNode(node) {
+          var inertNode = this._inertManager.register(node, this);
+          this._managedNodes.add(inertNode);
+        }
+
+        /**
+         * Unregister the given node with this InertRoot and with InertManager.
+         * @param {!Node} node
+         */
+
+      }, {
+        key: '_unmanageNode',
+        value: function _unmanageNode(node) {
+          var inertNode = this._inertManager.deregister(node, this);
+          if (inertNode) {
+            this._managedNodes['delete'](inertNode);
+          }
+        }
+
+        /**
+         * Unregister the entire subtree starting at `startNode`.
+         * @param {!Node} startNode
+         */
+
+      }, {
+        key: '_unmanageSubtree',
+        value: function _unmanageSubtree(startNode) {
+          var _this3 = this;
+
+          composedTreeWalk(startNode, function (node) {
+            return _this3._unmanageNode(node);
+          });
+        }
+
+        /**
+         * If a descendant node is found with an `inert` attribute, adopt its managed nodes.
+         * @param {!HTMLElement} node
+         */
+
+      }, {
+        key: '_adoptInertRoot',
+        value: function _adoptInertRoot(node) {
+          var inertSubroot = this._inertManager.getInertRoot(node);
+
+          // During initialisation this inert root may not have been registered yet,
+          // so register it now if need be.
+          if (!inertSubroot) {
+            this._inertManager.setInert(node, true);
+            inertSubroot = this._inertManager.getInertRoot(node);
+          }
+
+          inertSubroot.managedNodes.forEach(function (savedInertNode) {
+            this._manageNode(savedInertNode.node);
+          }, this);
+        }
+
+        /**
+         * Callback used when mutation observer detects subtree additions, removals, or attribute changes.
+         * @param {!Array<!MutationRecord>} records
+         * @param {!MutationObserver} self
+         */
+
+      }, {
+        key: '_onMutation',
+        value: function _onMutation(records, self) {
+          records.forEach(function (record) {
+            var target = /** @type {!HTMLElement} */record.target;
+            if (record.type === 'childList') {
+              // Manage added nodes
+              slice.call(record.addedNodes).forEach(function (node) {
+                this._makeSubtreeUnfocusable(node);
+              }, this);
+
+              // Un-manage removed nodes
+              slice.call(record.removedNodes).forEach(function (node) {
+                this._unmanageSubtree(node);
+              }, this);
+            } else if (record.type === 'attributes') {
+              if (record.attributeName === 'tabindex') {
+                // Re-initialise inert node if tabindex changes
+                this._manageNode(target);
+              } else if (target !== this._rootElement && record.attributeName === 'inert' && target.hasAttribute('inert')) {
+                // If a new inert root is added, adopt its managed nodes and make sure it knows about the
+                // already managed nodes from this inert subroot.
+                this._adoptInertRoot(target);
+                var inertSubroot = this._inertManager.getInertRoot(target);
+                this._managedNodes.forEach(function (managedNode) {
+                  if (target.contains(managedNode.node)) {
+                    inertSubroot._manageNode(managedNode.node);
+                  }
+                });
+              }
+            }
+          }, this);
+        }
+      }, {
+        key: 'managedNodes',
+        get: function get() {
+          return new Set(this._managedNodes);
+        }
+
+        /** @return {boolean} */
+
+      }, {
+        key: 'hasSavedAriaHidden',
+        get: function get() {
+          return this._savedAriaHidden !== null;
+        }
+
+        /** @param {?string} ariaHidden */
+
+      }, {
+        key: 'savedAriaHidden',
+        set: function set(ariaHidden) {
+          this._savedAriaHidden = ariaHidden;
+        }
+
+        /** @return {?string} */
+        ,
+        get: function get() {
+          return this._savedAriaHidden;
+        }
+      }]);
+
+      return InertRoot;
+    }();
+
+    /**
+     * `InertNode` initialises and manages a single inert node.
+     * A node is inert if it is a descendant of one or more inert root elements.
+     *
+     * On construction, `InertNode` saves the existing `tabindex` value for the node, if any, and
+     * either removes the `tabindex` attribute or sets it to `-1`, depending on whether the element
+     * is intrinsically focusable or not.
+     *
+     * `InertNode` maintains a set of `InertRoot`s which are descendants of this `InertNode`. When an
+     * `InertRoot` is destroyed, and calls `InertManager.deregister()`, the `InertManager` notifies the
+     * `InertNode` via `removeInertRoot()`, which in turn destroys the `InertNode` if no `InertRoot`s
+     * remain in the set. On destruction, `InertNode` reinstates the stored `tabindex` if one exists,
+     * or removes the `tabindex` attribute if the element is intrinsically focusable.
+     */
+
+
+    var InertNode = function () {
+      /**
+       * @param {!Node} node A focusable element to be made inert.
+       * @param {!InertRoot} inertRoot The inert root element associated with this inert node.
+       */
+      function InertNode(node, inertRoot) {
+        _classCallCheck(this, InertNode);
+
+        /** @type {!Node} */
+        this._node = node;
+
+        /** @type {boolean} */
+        this._overrodeFocusMethod = false;
+
+        /**
+         * @type {!Set<!InertRoot>} The set of descendant inert roots.
+         *    If and only if this set becomes empty, this node is no longer inert.
+         */
+        this._inertRoots = new Set([inertRoot]);
+
+        /** @type {?number} */
+        this._savedTabIndex = null;
+
+        /** @type {boolean} */
+        this._destroyed = false;
+
+        // Save any prior tabindex info and make this node untabbable
+        this.ensureUntabbable();
+      }
+
+      /**
+       * Call this whenever this object is about to become obsolete.
+       * This makes the managed node focusable again and deletes all of the previously stored state.
+       */
+
+
+      _createClass(InertNode, [{
+        key: 'destructor',
+        value: function destructor() {
+          this._throwIfDestroyed();
+
+          if (this._node && this._node.nodeType === Node.ELEMENT_NODE) {
+            var element = /** @type {!HTMLElement} */this._node;
+            if (this._savedTabIndex !== null) {
+              element.setAttribute('tabindex', this._savedTabIndex);
+            } else {
+              element.removeAttribute('tabindex');
+            }
+
+            // Use `delete` to restore native focus method.
+            if (this._overrodeFocusMethod) {
+              delete element.focus;
+            }
+          }
+
+          // See note in InertRoot.destructor for why we cast these nulls to ANY.
+          this._node = /** @type {?} */null;
+          this._inertRoots = /** @type {?} */null;
+          this._destroyed = true;
+        }
+
+        /**
+         * @type {boolean} Whether this object is obsolete because the managed node is no longer inert.
+         * If the object has been destroyed, any attempt to access it will cause an exception.
+         */
+
+      }, {
+        key: '_throwIfDestroyed',
+
+
+        /**
+         * Throw if user tries to access destroyed InertNode.
+         */
+        value: function _throwIfDestroyed() {
+          if (this.destroyed) {
+            throw new Error('Trying to access destroyed InertNode');
+          }
+        }
+
+        /** @return {boolean} */
+
+      }, {
+        key: 'ensureUntabbable',
+
+
+        /** Save the existing tabindex value and make the node untabbable and unfocusable */
+        value: function ensureUntabbable() {
+          if (this.node.nodeType !== Node.ELEMENT_NODE) {
+            return;
+          }
+          var element = /** @type {!HTMLElement} */this.node;
+          if (matches.call(element, _focusableElementsString)) {
+            if ( /** @type {!HTMLElement} */element.tabIndex === -1 && this.hasSavedTabIndex) {
+              return;
+            }
+
+            if (element.hasAttribute('tabindex')) {
+              this._savedTabIndex = /** @type {!HTMLElement} */element.tabIndex;
+            }
+            element.setAttribute('tabindex', '-1');
+            if (element.nodeType === Node.ELEMENT_NODE) {
+              element.focus = function () {};
+              this._overrodeFocusMethod = true;
+            }
+          } else if (element.hasAttribute('tabindex')) {
+            this._savedTabIndex = /** @type {!HTMLElement} */element.tabIndex;
+            element.removeAttribute('tabindex');
+          }
+        }
+
+        /**
+         * Add another inert root to this inert node's set of managing inert roots.
+         * @param {!InertRoot} inertRoot
+         */
+
+      }, {
+        key: 'addInertRoot',
+        value: function addInertRoot(inertRoot) {
+          this._throwIfDestroyed();
+          this._inertRoots.add(inertRoot);
+        }
+
+        /**
+         * Remove the given inert root from this inert node's set of managing inert roots.
+         * If the set of managing inert roots becomes empty, this node is no longer inert,
+         * so the object should be destroyed.
+         * @param {!InertRoot} inertRoot
+         */
+
+      }, {
+        key: 'removeInertRoot',
+        value: function removeInertRoot(inertRoot) {
+          this._throwIfDestroyed();
+          this._inertRoots['delete'](inertRoot);
+          if (this._inertRoots.size === 0) {
+            this.destructor();
+          }
+        }
+      }, {
+        key: 'destroyed',
+        get: function get() {
+          return (/** @type {!InertNode} */this._destroyed
+          );
+        }
+      }, {
+        key: 'hasSavedTabIndex',
+        get: function get() {
+          return this._savedTabIndex !== null;
+        }
+
+        /** @return {!Node} */
+
+      }, {
+        key: 'node',
+        get: function get() {
+          this._throwIfDestroyed();
+          return this._node;
+        }
+
+        /** @param {?number} tabIndex */
+
+      }, {
+        key: 'savedTabIndex',
+        set: function set(tabIndex) {
+          this._throwIfDestroyed();
+          this._savedTabIndex = tabIndex;
+        }
+
+        /** @return {?number} */
+        ,
+        get: function get() {
+          this._throwIfDestroyed();
+          return this._savedTabIndex;
+        }
+      }]);
+
+      return InertNode;
+    }();
+
+    /**
+     * InertManager is a per-document singleton object which manages all inert roots and nodes.
+     *
+     * When an element becomes an inert root by having an `inert` attribute set and/or its `inert`
+     * property set to `true`, the `setInert` method creates an `InertRoot` object for the element.
+     * The `InertRoot` in turn registers itself as managing all of the element's focusable descendant
+     * nodes via the `register()` method. The `InertManager` ensures that a single `InertNode` instance
+     * is created for each such node, via the `_managedNodes` map.
+     */
+
+
+    var InertManager = function () {
+      /**
+       * @param {!Document} document
+       */
+      function InertManager(document) {
+        _classCallCheck(this, InertManager);
+
+        if (!document) {
+          throw new Error('Missing required argument; InertManager needs to wrap a document.');
+        }
+
+        /** @type {!Document} */
+        this._document = document;
+
+        /**
+         * All managed nodes known to this InertManager. In a map to allow looking up by Node.
+         * @type {!Map<!Node, !InertNode>}
+         */
+        this._managedNodes = new Map();
+
+        /**
+         * All inert roots known to this InertManager. In a map to allow looking up by Node.
+         * @type {!Map<!Node, !InertRoot>}
+         */
+        this._inertRoots = new Map();
+
+        /**
+         * Observer for mutations on `document.body`.
+         * @type {!MutationObserver}
+         */
+        this._observer = new MutationObserver(this._watchForInert.bind(this));
+
+        // Add inert style.
+        addInertStyle(document.head || document.body || document.documentElement);
+
+        // Wait for document to be loaded.
+        if (document.readyState === 'loading') {
+          document.addEventListener('DOMContentLoaded', this._onDocumentLoaded.bind(this));
+        } else {
+          this._onDocumentLoaded();
+        }
+      }
+
+      /**
+       * Set whether the given element should be an inert root or not.
+       * @param {!HTMLElement} root
+       * @param {boolean} inert
+       */
+
+
+      _createClass(InertManager, [{
+        key: 'setInert',
+        value: function setInert(root, inert) {
+          if (inert) {
+            if (this._inertRoots.has(root)) {
+              // element is already inert
+              return;
+            }
+
+            var inertRoot = new InertRoot(root, this);
+            root.setAttribute('inert', '');
+            this._inertRoots.set(root, inertRoot);
+            // If not contained in the document, it must be in a shadowRoot.
+            // Ensure inert styles are added there.
+            if (!this._document.body.contains(root)) {
+              var parent = root.parentNode;
+              while (parent) {
+                if (parent.nodeType === 11) {
+                  addInertStyle(parent);
+                }
+                parent = parent.parentNode;
+              }
+            }
+          } else {
+            if (!this._inertRoots.has(root)) {
+              // element is already non-inert
+              return;
+            }
+
+            var _inertRoot = this._inertRoots.get(root);
+            _inertRoot.destructor();
+            this._inertRoots['delete'](root);
+            root.removeAttribute('inert');
+          }
+        }
+
+        /**
+         * Get the InertRoot object corresponding to the given inert root element, if any.
+         * @param {!Node} element
+         * @return {!InertRoot|undefined}
+         */
+
+      }, {
+        key: 'getInertRoot',
+        value: function getInertRoot(element) {
+          return this._inertRoots.get(element);
+        }
+
+        /**
+         * Register the given InertRoot as managing the given node.
+         * In the case where the node has a previously existing inert root, this inert root will
+         * be added to its set of inert roots.
+         * @param {!Node} node
+         * @param {!InertRoot} inertRoot
+         * @return {!InertNode} inertNode
+         */
+
+      }, {
+        key: 'register',
+        value: function register(node, inertRoot) {
+          var inertNode = this._managedNodes.get(node);
+          if (inertNode !== undefined) {
+            // node was already in an inert subtree
+            inertNode.addInertRoot(inertRoot);
+          } else {
+            inertNode = new InertNode(node, inertRoot);
+          }
+
+          this._managedNodes.set(node, inertNode);
+
+          return inertNode;
+        }
+
+        /**
+         * De-register the given InertRoot as managing the given inert node.
+         * Removes the inert root from the InertNode's set of managing inert roots, and remove the inert
+         * node from the InertManager's set of managed nodes if it is destroyed.
+         * If the node is not currently managed, this is essentially a no-op.
+         * @param {!Node} node
+         * @param {!InertRoot} inertRoot
+         * @return {?InertNode} The potentially destroyed InertNode associated with this node, if any.
+         */
+
+      }, {
+        key: 'deregister',
+        value: function deregister(node, inertRoot) {
+          var inertNode = this._managedNodes.get(node);
+          if (!inertNode) {
+            return null;
+          }
+
+          inertNode.removeInertRoot(inertRoot);
+          if (inertNode.destroyed) {
+            this._managedNodes['delete'](node);
+          }
+
+          return inertNode;
+        }
+
+        /**
+         * Callback used when document has finished loading.
+         */
+
+      }, {
+        key: '_onDocumentLoaded',
+        value: function _onDocumentLoaded() {
+          // Find all inert roots in document and make them actually inert.
+          var inertElements = slice.call(this._document.querySelectorAll('[inert]'));
+          inertElements.forEach(function (inertElement) {
+            this.setInert(inertElement, true);
+          }, this);
+
+          // Comment this out to use programmatic API only.
+          this._observer.observe(this._document.body || this._document.documentElement, { attributes: true, subtree: true, childList: true });
+        }
+
+        /**
+         * Callback used when mutation observer detects attribute changes.
+         * @param {!Array<!MutationRecord>} records
+         * @param {!MutationObserver} self
+         */
+
+      }, {
+        key: '_watchForInert',
+        value: function _watchForInert(records, self) {
+          var _this = this;
+          records.forEach(function (record) {
+            switch (record.type) {
+              case 'childList':
+                slice.call(record.addedNodes).forEach(function (node) {
+                  if (node.nodeType !== Node.ELEMENT_NODE) {
+                    return;
+                  }
+                  var inertElements = slice.call(node.querySelectorAll('[inert]'));
+                  if (matches.call(node, '[inert]')) {
+                    inertElements.unshift(node);
+                  }
+                  inertElements.forEach(function (inertElement) {
+                    this.setInert(inertElement, true);
+                  }, _this);
+                }, _this);
+                break;
+              case 'attributes':
+                if (record.attributeName !== 'inert') {
+                  return;
+                }
+                var target = /** @type {!HTMLElement} */record.target;
+                var inert = target.hasAttribute('inert');
+                _this.setInert(target, inert);
+                break;
+            }
+          }, this);
+        }
+      }]);
+
+      return InertManager;
+    }();
+
+    /**
+     * Recursively walk the composed tree from |node|.
+     * @param {!Node} node
+     * @param {(function (!HTMLElement))=} callback Callback to be called for each element traversed,
+     *     before descending into child nodes.
+     * @param {?ShadowRoot=} shadowRootAncestor The nearest ShadowRoot ancestor, if any.
+     */
+
+
+    function composedTreeWalk(node, callback, shadowRootAncestor) {
+      if (node.nodeType == Node.ELEMENT_NODE) {
+        var element = /** @type {!HTMLElement} */node;
+        if (callback) {
+          callback(element);
+        }
+
+        // Descend into node:
+        // If it has a ShadowRoot, ignore all child elements - these will be picked
+        // up by the <content> or <shadow> elements. Descend straight into the
+        // ShadowRoot.
+        var shadowRoot = /** @type {!HTMLElement} */element.shadowRoot;
+        if (shadowRoot) {
+          composedTreeWalk(shadowRoot, callback, shadowRoot);
+          return;
+        }
+
+        // If it is a <content> element, descend into distributed elements - these
+        // are elements from outside the shadow root which are rendered inside the
+        // shadow DOM.
+        if (element.localName == 'content') {
+          var content = /** @type {!HTMLContentElement} */element;
+          // Verifies if ShadowDom v0 is supported.
+          var distributedNodes = content.getDistributedNodes ? content.getDistributedNodes() : [];
+          for (var i = 0; i < distributedNodes.length; i++) {
+            composedTreeWalk(distributedNodes[i], callback, shadowRootAncestor);
+          }
+          return;
+        }
+
+        // If it is a <slot> element, descend into assigned nodes - these
+        // are elements from outside the shadow root which are rendered inside the
+        // shadow DOM.
+        if (element.localName == 'slot') {
+          var slot = /** @type {!HTMLSlotElement} */element;
+          // Verify if ShadowDom v1 is supported.
+          var _distributedNodes = slot.assignedNodes ? slot.assignedNodes({ flatten: true }) : [];
+          for (var _i = 0; _i < _distributedNodes.length; _i++) {
+            composedTreeWalk(_distributedNodes[_i], callback, shadowRootAncestor);
+          }
+          return;
+        }
+      }
+
+      // If it is neither the parent of a ShadowRoot, a <content> element, a <slot>
+      // element, nor a <shadow> element recurse normally.
+      var child = node.firstChild;
+      while (child != null) {
+        composedTreeWalk(child, callback, shadowRootAncestor);
+        child = child.nextSibling;
+      }
+    }
+
+    /**
+     * Adds a style element to the node containing the inert specific styles
+     * @param {!Node} node
+     */
+    function addInertStyle(node) {
+      if (node.querySelector('style#inert-style, link#inert-style')) {
+        return;
+      }
+      var style = document.createElement('style');
+      style.setAttribute('id', 'inert-style');
+      style.textContent = '\n' + '[inert] {\n' + '  pointer-events: none;\n' + '  cursor: default;\n' + '}\n' + '\n' + '[inert], [inert] * {\n' + '  -webkit-user-select: none;\n' + '  -moz-user-select: none;\n' + '  -ms-user-select: none;\n' + '  user-select: none;\n' + '}\n';
+      node.appendChild(style);
+    }
+
+    if (!HTMLElement.prototype.hasOwnProperty('inert')) {
+      /** @type {!InertManager} */
+      var inertManager = new InertManager(document);
+
+      Object.defineProperty(HTMLElement.prototype, 'inert', {
+        enumerable: true,
+        /** @this {!HTMLElement} */
+        get: function get() {
+          return this.hasAttribute('inert');
+        },
+        /** @this {!HTMLElement} */
+        set: function set(inert) {
+          inertManager.setInert(this, inert);
+        }
+      });
+    }
+  })();
+
+})));
diff --git a/wp-includes/js/dist/vendor/wp-polyfill-inert.min.js b/wp-includes/js/dist/vendor/wp-polyfill-inert.min.js
new file mode 100644
index 0000000000..56177202ee
--- /dev/null
+++ b/wp-includes/js/dist/vendor/wp-polyfill-inert.min.js
@@ -0,0 +1 @@
+!function(e){"object"==typeof exports&&"undefined"!=typeof module||"function"!=typeof define||!define.amd?e():define("inert",e)}((function(){"use strict";var e,t,n,i,o,r,s=function(e,t,n){return t&&a(e.prototype,t),n&&a(e,n),e};function a(e,t){for(var n=0;n<t.length;n++){var i=t[n];i.enumerable=i.enumerable||!1,i.configurable=!0,"value"in i&&(i.writable=!0),Object.defineProperty(e,i.key,i)}}function d(e,t){if(!(e instanceof t))throw new TypeError("Cannot call a class as a function")}function u(e,t){d(this,u),this._inertManager=t,this._rootElement=e,this._managedNodes=new Set,this._rootElement.hasAttribute("aria-hidden")?this._savedAriaHidden=this._rootElement.getAttribute("aria-hidden"):this._savedAriaHidden=null,this._rootElement.setAttribute("aria-hidden","true"),this._makeSubtreeUnfocusable(this._rootElement),this._observer=new MutationObserver(this._onMutation.bind(this)),this._observer.observe(this._rootElement,{attributes:!0,childList:!0,subtree:!0})}function h(e,t){d(this,h),this._node=e,this._overrodeFocusMethod=!1,this._inertRoots=new Set([t]),this._savedTabIndex=null,this._destroyed=!1,this.ensureUntabbable()}function l(e){if(d(this,l),!e)throw new Error("Missing required argument; InertManager needs to wrap a document.");this._document=e,this._managedNodes=new Map,this._inertRoots=new Map,this._observer=new MutationObserver(this._watchForInert.bind(this)),_(e.head||e.body||e.documentElement),"loading"===e.readyState?e.addEventListener("DOMContentLoaded",this._onDocumentLoaded.bind(this)):this._onDocumentLoaded()}function c(e,t,n){if(e.nodeType==Node.ELEMENT_NODE){var i=e;if(s=(t&&t(i),i.shadowRoot))return void c(s,t,s);if("content"==i.localName){for(var o=(s=i).getDistributedNodes?s.getDistributedNodes():[],r=0;r<o.length;r++)c(o[r],t,n);return}if("slot"==i.localName){for(var s,a=(s=i).assignedNodes?s.assignedNodes({flatten:!0}):[],d=0;d<a.length;d++)c(a[d],t,n);return}}for(var u=e.firstChild;null!=u;)c(u,t,n),u=u.nextSibling}function _(e){var t;e.querySelector("style#inert-style, link#inert-style")||((t=document.createElement("style")).setAttribute("id","inert-style"),t.textContent="\n[inert] {\n  pointer-events: none;\n  cursor: default;\n}\n\n[inert], [inert] * {\n  -webkit-user-select: none;\n  -moz-user-select: none;\n  -ms-user-select: none;\n  user-select: none;\n}\n",e.appendChild(t))}"undefined"!=typeof window&&(e=Array.prototype.slice,t=Element.prototype.matches||Element.prototype.msMatchesSelector,n=["a[href]","area[href]","input:not([disabled])","select:not([disabled])","textarea:not([disabled])","button:not([disabled])","details","summary","iframe","object","embed","[contenteditable]"].join(","),s(u,[{key:"destructor",value:function(){this._observer.disconnect(),this._rootElement&&(null!==this._savedAriaHidden?this._rootElement.setAttribute("aria-hidden",this._savedAriaHidden):this._rootElement.removeAttribute("aria-hidden")),this._managedNodes.forEach((function(e){this._unmanageNode(e.node)}),this),this._observer=null,this._rootElement=null,this._managedNodes=null,this._inertManager=null}},{key:"_makeSubtreeUnfocusable",value:function(e){var t=this,n=(c(e,(function(e){return t._visitNode(e)})),document.activeElement);if(!document.body.contains(e)){for(var i=e,o=void 0;i;){if(i.nodeType===Node.DOCUMENT_FRAGMENT_NODE){o=i;break}i=i.parentNode}o&&(n=o.activeElement)}e.contains(n)&&(n.blur(),n===document.activeElement&&document.body.focus())}},{key:"_visitNode",value:function(e){e.nodeType===Node.ELEMENT_NODE&&(e!==this._rootElement&&e.hasAttribute("inert")&&this._adoptInertRoot(e),(t.call(e,n)||e.hasAttribute("tabindex"))&&this._manageNode(e))}},{key:"_manageNode",value:function(e){e=this._inertManager.register(e,this),this._managedNodes.add(e)}},{key:"_unmanageNode",value:function(e){(e=this._inertManager.deregister(e,this))&&this._managedNodes.delete(e)}},{key:"_unmanageSubtree",value:function(e){var t=this;c(e,(function(e){return t._unmanageNode(e)}))}},{key:"_adoptInertRoot",value:function(e){var t=this._inertManager.getInertRoot(e);t||(this._inertManager.setInert(e,!0),t=this._inertManager.getInertRoot(e)),t.managedNodes.forEach((function(e){this._manageNode(e.node)}),this)}},{key:"_onMutation",value:function(t,n){t.forEach((function(t){var n,i=t.target;"childList"===t.type?(e.call(t.addedNodes).forEach((function(e){this._makeSubtreeUnfocusable(e)}),this),e.call(t.removedNodes).forEach((function(e){this._unmanageSubtree(e)}),this)):"attributes"===t.type&&("tabindex"===t.attributeName?this._manageNode(i):i!==this._rootElement&&"inert"===t.attributeName&&i.hasAttribute("inert")&&(this._adoptInertRoot(i),n=this._inertManager.getInertRoot(i),this._managedNodes.forEach((function(e){i.contains(e.node)&&n._manageNode(e.node)}))))}),this)}},{key:"managedNodes",get:function(){return new Set(this._managedNodes)}},{key:"hasSavedAriaHidden",get:function(){return null!==this._savedAriaHidden}},{key:"savedAriaHidden",set:function(e){this._savedAriaHidden=e},get:function(){return this._savedAriaHidden}}]),i=u,s(h,[{key:"destructor",value:function(){var e;this._throwIfDestroyed(),this._node&&this._node.nodeType===Node.ELEMENT_NODE&&(e=this._node,null!==this._savedTabIndex?e.setAttribute("tabindex",this._savedTabIndex):e.removeAttribute("tabindex"),this._overrodeFocusMethod&&delete e.focus),this._node=null,this._inertRoots=null,this._destroyed=!0}},{key:"_throwIfDestroyed",value:function(){if(this.destroyed)throw new Error("Trying to access destroyed InertNode")}},{key:"ensureUntabbable",value:function(){var e;this.node.nodeType===Node.ELEMENT_NODE&&(e=this.node,t.call(e,n)?-1===e.tabIndex&&this.hasSavedTabIndex||(e.hasAttribute("tabindex")&&(this._savedTabIndex=e.tabIndex),e.setAttribute("tabindex","-1"),e.nodeType===Node.ELEMENT_NODE&&(e.focus=function(){},this._overrodeFocusMethod=!0)):e.hasAttribute("tabindex")&&(this._savedTabIndex=e.tabIndex,e.removeAttribute("tabindex")))}},{key:"addInertRoot",value:function(e){this._throwIfDestroyed(),this._inertRoots.add(e)}},{key:"removeInertRoot",value:function(e){this._throwIfDestroyed(),this._inertRoots.delete(e),0===this._inertRoots.size&&this.destructor()}},{key:"destroyed",get:function(){return this._destroyed}},{key:"hasSavedTabIndex",get:function(){return null!==this._savedTabIndex}},{key:"node",get:function(){return this._throwIfDestroyed(),this._node}},{key:"savedTabIndex",set:function(e){this._throwIfDestroyed(),this._savedTabIndex=e},get:function(){return this._throwIfDestroyed(),this._savedTabIndex}}]),o=h,s(l,[{key:"setInert",value:function(e,t){if(t){if(!this._inertRoots.has(e)&&(t=new i(e,this),e.setAttribute("inert",""),this._inertRoots.set(e,t),!this._document.body.contains(e)))for(var n=e.parentNode;n;)11===n.nodeType&&_(n),n=n.parentNode}else this._inertRoots.has(e)&&(this._inertRoots.get(e).destructor(),this._inertRoots.delete(e),e.removeAttribute("inert"))}},{key:"getInertRoot",value:function(e){return this._inertRoots.get(e)}},{key:"register",value:function(e,t){var n=this._managedNodes.get(e);return void 0!==n?n.addInertRoot(t):n=new o(e,t),this._managedNodes.set(e,n),n}},{key:"deregister",value:function(e,t){var n=this._managedNodes.get(e);return n?(n.removeInertRoot(t),n.destroyed&&this._managedNodes.delete(e),n):null}},{key:"_onDocumentLoaded",value:function(){e.call(this._document.querySelectorAll("[inert]")).forEach((function(e){this.setInert(e,!0)}),this),this._observer.observe(this._document.body||this._document.documentElement,{attributes:!0,subtree:!0,childList:!0})}},{key:"_watchForInert",value:function(n,i){var o=this;n.forEach((function(n){switch(n.type){case"childList":e.call(n.addedNodes).forEach((function(n){var i;n.nodeType===Node.ELEMENT_NODE&&(i=e.call(n.querySelectorAll("[inert]")),t.call(n,"[inert]")&&i.unshift(n),i.forEach((function(e){this.setInert(e,!0)}),o))}),o);break;case"attributes":if("inert"!==n.attributeName)return;var i=n.target,r=i.hasAttribute("inert");o.setInert(i,r)}}),this)}}]),s=l,HTMLElement.prototype.hasOwnProperty("inert")||(r=new s(document),Object.defineProperty(HTMLElement.prototype,"inert",{enumerable:!0,get:function(){return this.hasAttribute("inert")},set:function(e){r.setInert(this,e)}})))}));
\ No newline at end of file
diff --git a/wp-includes/script-loader.php b/wp-includes/script-loader.php
index 093d52b284..1444727f9d 100644
--- a/wp-includes/script-loader.php
+++ b/wp-includes/script-loader.php
@@ -99,7 +99,8 @@ function wp_default_packages_vendor( $scripts ) {
 		'wp-polyfill-dom-rect',
 		'wp-polyfill-element-closest',
 		'wp-polyfill-object-fit',
-		'wp-polyfill' => array( 'regenerator-runtime' ),
+		'wp-polyfill-inert',
+		'wp-polyfill' => array( 'wp-polyfill-inert', 'regenerator-runtime' ),
 	);
 
 	$vendor_scripts_versions = array(
@@ -115,6 +116,7 @@ function wp_default_packages_vendor( $scripts ) {
 		'wp-polyfill-dom-rect'        => '4.4.0',
 		'wp-polyfill-element-closest' => '2.0.2',
 		'wp-polyfill-object-fit'      => '2.3.5',
+		'wp-polyfill-inert'           => '3.1.2',
 		'wp-polyfill'                 => '3.15.0',
 	);
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 95ca57f5ca..94231f4f5b 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.2-alpha-55083';
+$wp_version = '6.2-alpha-55084';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.