Modal

    <div>
  <dialog class="gg-c-modal">
    <div class="gg-c-modal__header">
      <h2 class="gg-c-modal__main-title">Plan Details</h2>
      <button class="gg-c-modal__close-button">
        <span class="gg-u-screen-reader-only">Close</span>
        <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M13 11.9l1.1-1.1c1.3-1.2 3.1-2.8 4.3-4.2.3-.4.4-.4.1-.9-.2-.4-.8-.6-1.2-.2-1.8 1.8-3.5 3.6-5.3 5.4l-1-1C9.8 8.8 8.7 7.6 7.5 6.4c-.3-.2-.9-1.2-1.5-.8-.4.3-.5.8-.2 1.2 1.7 1.8 3.4 3.5 5.1 5.1l-1.4 1.4c-.8.8-2.8 2.5-3.9 3.9-.6.8.3 1.7 1 1 1.2-1 3-2.9 3.9-3.9.5-.5.9-1 1.4-1.4l1.7 1.7c.9 1 2.6 2.8 3.4 3.5 1 .8 1.9-.3 1-1.1-1.4-1.3-3.3-3.3-5-5.1z" fill="#1d1d1b"/></svg>
      </button>
    </div>
    <div class="gg-c-modal__content">
      <p>
        Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras in libero
        eget sapien elementum egestas ultrices at lacus. Morbi eu urna diam. Nulla
        metus tortor, pellentesque id nisl vel, tempus placerat mauris. Etiam odio
        lectus, molestie sed odio vitae, mollis ullamcorper dolor. Morbi
        vestibulum est quis nunc laoreet, ut pellentesque ante aliquam. Nulla orci
        nulla, varius a orci sed, sodales malesuada augue. Vivamus sodales tellus
        ac ligula gravida aliquam. Integer sagittis porta augue, sed posuere nisi
        ornare eu. Cras volutpat elit leo, ut facilisis quam vehicula at.
      </p>
    </div>
  </dialog>

  <button data-target="showModal" class="gg-c-btn gg-c-btn--primary">
    <span class="gg-c-btn__switch">Show modal</span>
  </button>
</div>

<script>
  (function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
  typeof define === 'function' && define.amd ? define(factory) :
  (global = global || self, global.dialogPolyfill = factory());
}(this, function () { 'use strict';

  // nb. This is for IE10 and lower _only_.
  var supportCustomEvent = window.CustomEvent;
  if (!supportCustomEvent || typeof supportCustomEvent === 'object') {
    supportCustomEvent = function CustomEvent(event, x) {
      x = x || {};
      var ev = document.createEvent('CustomEvent');
      ev.initCustomEvent(event, !!x.bubbles, !!x.cancelable, x.detail || null);
      return ev;
    };
    supportCustomEvent.prototype = window.Event.prototype;
  }

  /**
   * @param {Element} el to check for stacking context
   * @return {boolean} whether this el or its parents creates a stacking context
   */
  function createsStackingContext(el) {
    while (el && el !== document.body) {
      var s = window.getComputedStyle(el);
      var invalid = function(k, ok) {
        return !(s[k] === undefined || s[k] === ok);
      };
      
      if (s.opacity < 1 ||
          invalid('zIndex', 'auto') ||
          invalid('transform', 'none') ||
          invalid('mixBlendMode', 'normal') ||
          invalid('filter', 'none') ||
          invalid('perspective', 'none') ||
          s['isolation'] === 'isolate' ||
          s.position === 'fixed' ||
          s.webkitOverflowScrolling === 'touch') {
        return true;
      }
      el = el.parentElement;
    }
    return false;
  }

  /**
   * Finds the nearest <dialog> from the passed element.
   *
   * @param {Element} el to search from
   * @return {HTMLDialogElement} dialog found
   */
  function findNearestDialog(el) {
    while (el) {
      if (el.localName === 'dialog') {
        return /** @type {HTMLDialogElement} */ (el);
      }
      el = el.parentElement;
    }
    return null;
  }

  /**
   * Blur the specified element, as long as it's not the HTML body element.
   * This works around an IE9/10 bug - blurring the body causes Windows to
   * blur the whole application.
   *
   * @param {Element} el to blur
   */
  function safeBlur(el) {
    if (el && el.blur && el !== document.body) {
      el.blur();
    }
  }

  /**
   * @param {!NodeList} nodeList to search
   * @param {Node} node to find
   * @return {boolean} whether node is inside nodeList
   */
  function inNodeList(nodeList, node) {
    for (var i = 0; i < nodeList.length; ++i) {
      if (nodeList[i] === node) {
        return true;
      }
    }
    return false;
  }

  /**
   * @param {HTMLFormElement} el to check
   * @return {boolean} whether this form has method="dialog"
   */
  function isFormMethodDialog(el) {
    if (!el || !el.hasAttribute('method')) {
      return false;
    }
    return el.getAttribute('method').toLowerCase() === 'dialog';
  }

  /**
   * @param {!HTMLDialogElement} dialog to upgrade
   * @constructor
   */
  function dialogPolyfillInfo(dialog) {
    this.dialog_ = dialog;
    this.replacedStyleTop_ = false;
    this.openAsModal_ = false;

    // Set a11y role. Browsers that support dialog implicitly know this already.
    if (!dialog.hasAttribute('role')) {
      dialog.setAttribute('role', 'dialog');
    }

    dialog.show = this.show.bind(this);
    dialog.showModal = this.showModal.bind(this);
    dialog.close = this.close.bind(this);

    if (!('returnValue' in dialog)) {
      dialog.returnValue = '';
    }

    if ('MutationObserver' in window) {
      var mo = new MutationObserver(this.maybeHideModal.bind(this));
      mo.observe(dialog, {attributes: true, attributeFilter: ['open']});
    } else {
      // IE10 and below support. Note that DOMNodeRemoved etc fire _before_ removal. They also
      // seem to fire even if the element was removed as part of a parent removal. Use the removed
      // events to force downgrade (useful if removed/immediately added).
      var removed = false;
      var cb = function() {
        removed ? this.downgradeModal() : this.maybeHideModal();
        removed = false;
      }.bind(this);
      var timeout;
      var delayModel = function(ev) {
        if (ev.target !== dialog) { return; }  // not for a child element
        var cand = 'DOMNodeRemoved';
        removed |= (ev.type.substr(0, cand.length) === cand);
        window.clearTimeout(timeout);
        timeout = window.setTimeout(cb, 0);
      };
      ['DOMAttrModified', 'DOMNodeRemoved', 'DOMNodeRemovedFromDocument'].forEach(function(name) {
        dialog.addEventListener(name, delayModel);
      });
    }
    // Note that the DOM is observed inside DialogManager while any dialog
    // is being displayed as a modal, to catch modal removal from the DOM.

    Object.defineProperty(dialog, 'open', {
      set: this.setOpen.bind(this),
      get: dialog.hasAttribute.bind(dialog, 'open')
    });

    this.backdrop_ = document.createElement('div');
    this.backdrop_.className = 'backdrop';
    this.backdrop_.addEventListener('click', this.backdropClick_.bind(this));
  }

  dialogPolyfillInfo.prototype = {

    get dialog() {
      return this.dialog_;
    },

    /**
     * Maybe remove this dialog from the modal top layer. This is called when
     * a modal dialog may no longer be tenable, e.g., when the dialog is no
     * longer open or is no longer part of the DOM.
     */
    maybeHideModal: function() {
      if (this.dialog_.hasAttribute('open') && document.body.contains(this.dialog_)) { return; }
      this.downgradeModal();
    },

    /**
     * Remove this dialog from the modal top layer, leaving it as a non-modal.
     */
    downgradeModal: function() {
      if (!this.openAsModal_) { return; }
      this.openAsModal_ = false;
      this.dialog_.style.zIndex = '';

      // This won't match the native <dialog> exactly because if the user set top on a centered
      // polyfill dialog, that top gets thrown away when the dialog is closed. Not sure it's
      // possible to polyfill this perfectly.
      if (this.replacedStyleTop_) {
        this.dialog_.style.top = '';
        this.replacedStyleTop_ = false;
      }

      // Clear the backdrop and remove from the manager.
      this.backdrop_.parentNode && this.backdrop_.parentNode.removeChild(this.backdrop_);
      dialogPolyfill.dm.removeDialog(this);
    },

    /**
     * @param {boolean} value whether to open or close this dialog
     */
    setOpen: function(value) {
      if (value) {
        this.dialog_.hasAttribute('open') || this.dialog_.setAttribute('open', '');
      } else {
        this.dialog_.removeAttribute('open');
        this.maybeHideModal();  // nb. redundant with MutationObserver
      }
    },

    /**
     * Handles clicks on the fake .backdrop element, redirecting them as if
     * they were on the dialog itself.
     *
     * @param {!Event} e to redirect
     */
    backdropClick_: function(e) {
      if (!this.dialog_.hasAttribute('tabindex')) {
        // Clicking on the backdrop should move the implicit cursor, even if dialog cannot be
        // focused. Create a fake thing to focus on. If the backdrop was _before_ the dialog, this
        // would not be needed - clicks would move the implicit cursor there.
        var fake = document.createElement('div');
        this.dialog_.insertBefore(fake, this.dialog_.firstChild);
        fake.tabIndex = -1;
        fake.focus();
        this.dialog_.removeChild(fake);
      } else {
        this.dialog_.focus();
      }

      var redirectedEvent = document.createEvent('MouseEvents');
      redirectedEvent.initMouseEvent(e.type, e.bubbles, e.cancelable, window,
          e.detail, e.screenX, e.screenY, e.clientX, e.clientY, e.ctrlKey,
          e.altKey, e.shiftKey, e.metaKey, e.button, e.relatedTarget);
      this.dialog_.dispatchEvent(redirectedEvent);
      e.stopPropagation();
    },

    /**
     * Focuses on the first focusable element within the dialog. This will always blur the current
     * focus, even if nothing within the dialog is found.
     */
    focus_: function() {
      // Find element with `autofocus` attribute, or fall back to the first form/tabindex control.
      var target = this.dialog_.querySelector('[autofocus]:not([disabled])');
      if (!target && this.dialog_.tabIndex >= 0) {
        target = this.dialog_;
      }
      if (!target) {
        // Note that this is 'any focusable area'. This list is probably not exhaustive, but the
        // alternative involves stepping through and trying to focus everything.
        var opts = ['button', 'input', 'keygen', 'select', 'textarea'];
        var query = opts.map(function(el) {
          return el + ':not([disabled])';
        });
        // TODO(samthor): tabindex values that are not numeric are not focusable.
        query.push('[tabindex]:not([disabled]):not([tabindex=""])');  // tabindex != "", not disabled
        target = this.dialog_.querySelector(query.join(', '));
      }
      safeBlur(document.activeElement);
      target && target.focus();
    },

    /**
     * Sets the zIndex for the backdrop and dialog.
     *
     * @param {number} dialogZ
     * @param {number} backdropZ
     */
    updateZIndex: function(dialogZ, backdropZ) {
      if (dialogZ < backdropZ) {
        throw new Error('dialogZ should never be < backdropZ');
      }
      this.dialog_.style.zIndex = dialogZ;
      this.backdrop_.style.zIndex = backdropZ;
    },

    /**
     * Shows the dialog. If the dialog is already open, this does nothing.
     */
    show: function() {
      if (!this.dialog_.open) {
        this.setOpen(true);
        this.focus_();
      }
    },

    /**
     * Show this dialog modally.
     */
    showModal: function() {
      if (this.dialog_.hasAttribute('open')) {
        throw new Error('Failed to execute \'showModal\' on dialog: The element is already open, and therefore cannot be opened modally.');
      }
      if (!document.body.contains(this.dialog_)) {
        throw new Error('Failed to execute \'showModal\' on dialog: The element is not in a Document.');
      }
      if (!dialogPolyfill.dm.pushDialog(this)) {
        throw new Error('Failed to execute \'showModal\' on dialog: There are too many open modal dialogs.');
      }

      if (createsStackingContext(this.dialog_.parentElement)) {
        console.warn('A dialog is being shown inside a stacking context. ' +
            'This may cause it to be unusable. For more information, see this link: ' +
            'https://github.com/GoogleChrome/dialog-polyfill/#stacking-context');
      }

      this.setOpen(true);
      this.openAsModal_ = true;

      // Optionally center vertically, relative to the current viewport.
      if (dialogPolyfill.needsCentering(this.dialog_)) {
        dialogPolyfill.reposition(this.dialog_);
        this.replacedStyleTop_ = true;
      } else {
        this.replacedStyleTop_ = false;
      }

      // Insert backdrop.
      this.dialog_.parentNode.insertBefore(this.backdrop_, this.dialog_.nextSibling);

      // Focus on whatever inside the dialog.
      this.focus_();
    },

    /**
     * Closes this HTMLDialogElement. This is optional vs clearing the open
     * attribute, however this fires a 'close' event.
     *
     * @param {string=} opt_returnValue to use as the returnValue
     */
    close: function(opt_returnValue) {
      if (!this.dialog_.hasAttribute('open')) {
        throw new Error('Failed to execute \'close\' on dialog: The element does not have an \'open\' attribute, and therefore cannot be closed.');
      }
      this.setOpen(false);

      // Leave returnValue untouched in case it was set directly on the element
      if (opt_returnValue !== undefined) {
        this.dialog_.returnValue = opt_returnValue;
      }

      // Triggering "close" event for any attached listeners on the <dialog>.
      var closeEvent = new supportCustomEvent('close', {
        bubbles: false,
        cancelable: false
      });
    
      // If we have an onclose handler assigned and it's a function, call it
      if(this.dialog_.onclose instanceof Function) {
        this.dialog_.onclose(closeEvent);
      }

      // Dispatch the event as normal
      this.dialog_.dispatchEvent(closeEvent);

    }

  };

  var dialogPolyfill = {};

  dialogPolyfill.reposition = function(element) {
    var scrollTop = document.body.scrollTop || document.documentElement.scrollTop;
    var topValue = scrollTop + (window.innerHeight - element.offsetHeight) / 2;
    element.style.top = Math.max(scrollTop, topValue) + 'px';
  };

  dialogPolyfill.isInlinePositionSetByStylesheet = function(element) {
    for (var i = 0; i < document.styleSheets.length; ++i) {
      var styleSheet = document.styleSheets[i];
      var cssRules = null;
      // Some browsers throw on cssRules.
      try {
        cssRules = styleSheet.cssRules;
      } catch (e) {}
      if (!cssRules) { continue; }
      for (var j = 0; j < cssRules.length; ++j) {
        var rule = cssRules[j];
        var selectedNodes = null;
        // Ignore errors on invalid selector texts.
        try {
          selectedNodes = document.querySelectorAll(rule.selectorText);
        } catch(e) {}
        if (!selectedNodes || !inNodeList(selectedNodes, element)) {
          continue;
        }
        var cssTop = rule.style.getPropertyValue('top');
        var cssBottom = rule.style.getPropertyValue('bottom');
        if ((cssTop && cssTop !== 'auto') || (cssBottom && cssBottom !== 'auto')) {
          return true;
        }
      }
    }
    return false;
  };

  dialogPolyfill.needsCentering = function(dialog) {
    var computedStyle = window.getComputedStyle(dialog);
    if (computedStyle.position !== 'absolute') {
      return false;
    }

    // We must determine whether the top/bottom specified value is non-auto.  In
    // WebKit/Blink, checking computedStyle.top == 'auto' is sufficient, but
    // Firefox returns the used value. So we do this crazy thing instead: check
    // the inline style and then go through CSS rules.
    if ((dialog.style.top !== 'auto' && dialog.style.top !== '') ||
        (dialog.style.bottom !== 'auto' && dialog.style.bottom !== '')) {
      return false;
    }
    return !dialogPolyfill.isInlinePositionSetByStylesheet(dialog);
  };

  /**
   * @param {!Element} element to force upgrade
   */
  dialogPolyfill.forceRegisterDialog = function(element) {
    if (window.HTMLDialogElement || element.showModal) {
      console.warn('This browser already supports <dialog>, the polyfill ' +
          'may not work correctly', element);
    }
    if (element.localName !== 'dialog') {
      throw new Error('Failed to register dialog: The element is not a dialog.');
    }
    new dialogPolyfillInfo(/** @type {!HTMLDialogElement} */ (element));
  };

  /**
   * @param {!Element} element to upgrade, if necessary
   */
  dialogPolyfill.registerDialog = function(element) {
    if (!element.showModal) {
      dialogPolyfill.forceRegisterDialog(element);
    }
  };

  /**
   * @constructor
   */
  dialogPolyfill.DialogManager = function() {
    /** @type {!Array<!dialogPolyfillInfo>} */
    this.pendingDialogStack = [];

    var checkDOM = this.checkDOM_.bind(this);

    // The overlay is used to simulate how a modal dialog blocks the document.
    // The blocking dialog is positioned on top of the overlay, and the rest of
    // the dialogs on the pending dialog stack are positioned below it. In the
    // actual implementation, the modal dialog stacking is controlled by the
    // top layer, where z-index has no effect.
    this.overlay = document.createElement('div');
    this.overlay.className = '_dialog_overlay';
    this.overlay.addEventListener('click', function(e) {
      this.forwardTab_ = undefined;
      e.stopPropagation();
      checkDOM([]);  // sanity-check DOM
    }.bind(this));

    this.handleKey_ = this.handleKey_.bind(this);
    this.handleFocus_ = this.handleFocus_.bind(this);

    this.zIndexLow_ = 100000;
    this.zIndexHigh_ = 100000 + 150;

    this.forwardTab_ = undefined;

    if ('MutationObserver' in window) {
      this.mo_ = new MutationObserver(function(records) {
        var removed = [];
        records.forEach(function(rec) {
          for (var i = 0, c; c = rec.removedNodes[i]; ++i) {
            if (!(c instanceof Element)) {
              continue;
            } else if (c.localName === 'dialog') {
              removed.push(c);
            }
            removed = removed.concat(c.querySelectorAll('dialog'));
          }
        });
        removed.length && checkDOM(removed);
      });
    }
  };

  /**
   * Called on the first modal dialog being shown. Adds the overlay and related
   * handlers.
   */
  dialogPolyfill.DialogManager.prototype.blockDocument = function() {
    document.documentElement.addEventListener('focus', this.handleFocus_, true);
    document.addEventListener('keydown', this.handleKey_);
    this.mo_ && this.mo_.observe(document, {childList: true, subtree: true});
  };

  /**
   * Called on the first modal dialog being removed, i.e., when no more modal
   * dialogs are visible.
   */
  dialogPolyfill.DialogManager.prototype.unblockDocument = function() {
    document.documentElement.removeEventListener('focus', this.handleFocus_, true);
    document.removeEventListener('keydown', this.handleKey_);
    this.mo_ && this.mo_.disconnect();
  };

  /**
   * Updates the stacking of all known dialogs.
   */
  dialogPolyfill.DialogManager.prototype.updateStacking = function() {
    var zIndex = this.zIndexHigh_;

    for (var i = 0, dpi; dpi = this.pendingDialogStack[i]; ++i) {
      dpi.updateZIndex(--zIndex, --zIndex);
      if (i === 0) {
        this.overlay.style.zIndex = --zIndex;
      }
    }

    // Make the overlay a sibling of the dialog itself.
    var last = this.pendingDialogStack[0];
    if (last) {
      var p = last.dialog.parentNode || document.body;
      p.appendChild(this.overlay);
    } else if (this.overlay.parentNode) {
      this.overlay.parentNode.removeChild(this.overlay);
    }
  };

  /**
   * @param {Element} candidate to check if contained or is the top-most modal dialog
   * @return {boolean} whether candidate is contained in top dialog
   */
  dialogPolyfill.DialogManager.prototype.containedByTopDialog_ = function(candidate) {
    while (candidate = findNearestDialog(candidate)) {
      for (var i = 0, dpi; dpi = this.pendingDialogStack[i]; ++i) {
        if (dpi.dialog === candidate) {
          return i === 0;  // only valid if top-most
        }
      }
      candidate = candidate.parentElement;
    }
    return false;
  };

  dialogPolyfill.DialogManager.prototype.handleFocus_ = function(event) {
    if (this.containedByTopDialog_(event.target)) { return; }

    if (document.activeElement === document.documentElement) { return; }

    event.preventDefault();
    event.stopPropagation();
    safeBlur(/** @type {Element} */ (event.target));

    if (this.forwardTab_ === undefined) { return; }  // move focus only from a tab key

    var dpi = this.pendingDialogStack[0];
    var dialog = dpi.dialog;
    var position = dialog.compareDocumentPosition(event.target);
    if (position & Node.DOCUMENT_POSITION_PRECEDING) {
      if (this.forwardTab_) {
        // forward
        dpi.focus_();
      } else if (event.target !== document.documentElement) {
        // backwards if we're not already focused on <html>
        document.documentElement.focus();
      }
    }

    return false;
  };

  dialogPolyfill.DialogManager.prototype.handleKey_ = function(event) {
    this.forwardTab_ = undefined;
    if (event.keyCode === 27) {
      event.preventDefault();
      event.stopPropagation();
      var cancelEvent = new supportCustomEvent('cancel', {
        bubbles: false,
        cancelable: true
      });
      var dpi = this.pendingDialogStack[0];
      if (dpi && dpi.dialog.dispatchEvent(cancelEvent)) {
        dpi.dialog.close();
      }
    } else if (event.keyCode === 9) {
      this.forwardTab_ = !event.shiftKey;
    }
  };

  /**
   * Finds and downgrades any known modal dialogs that are no longer displayed. Dialogs that are
   * removed and immediately readded don't stay modal, they become normal.
   *
   * @param {!Array<!HTMLDialogElement>} removed that have definitely been removed
   */
  dialogPolyfill.DialogManager.prototype.checkDOM_ = function(removed) {
    // This operates on a clone because it may cause it to change. Each change also calls
    // updateStacking, which only actually needs to happen once. But who removes many modal dialogs
    // at a time?!
    var clone = this.pendingDialogStack.slice();
    clone.forEach(function(dpi) {
      if (removed.indexOf(dpi.dialog) !== -1) {
        dpi.downgradeModal();
      } else {
        dpi.maybeHideModal();
      }
    });
  };

  /**
   * @param {!dialogPolyfillInfo} dpi
   * @return {boolean} whether the dialog was allowed
   */
  dialogPolyfill.DialogManager.prototype.pushDialog = function(dpi) {
    var allowed = (this.zIndexHigh_ - this.zIndexLow_) / 2 - 1;
    if (this.pendingDialogStack.length >= allowed) {
      return false;
    }
    if (this.pendingDialogStack.unshift(dpi) === 1) {
      this.blockDocument();
    }
    this.updateStacking();
    return true;
  };

  /**
   * @param {!dialogPolyfillInfo} dpi
   */
  dialogPolyfill.DialogManager.prototype.removeDialog = function(dpi) {
    var index = this.pendingDialogStack.indexOf(dpi);
    if (index === -1) { return; }

    this.pendingDialogStack.splice(index, 1);
    if (this.pendingDialogStack.length === 0) {
      this.unblockDocument();
    }
    this.updateStacking();
  };

  dialogPolyfill.dm = new dialogPolyfill.DialogManager();
  dialogPolyfill.formSubmitter = null;
  dialogPolyfill.useValue = null;

  /**
   * Installs global handlers, such as click listers and native method overrides. These are needed
   * even if a no dialog is registered, as they deal with <form method="dialog">.
   */
  if (window.HTMLDialogElement === undefined) {

    /**
     * If HTMLFormElement translates method="DIALOG" into 'get', then replace the descriptor with
     * one that returns the correct value.
     */
    var testForm = document.createElement('form');
    testForm.setAttribute('method', 'dialog');
    if (testForm.method !== 'dialog') {
      var methodDescriptor = Object.getOwnPropertyDescriptor(HTMLFormElement.prototype, 'method');
      if (methodDescriptor) {
        // nb. Some older iOS and older PhantomJS fail to return the descriptor. Don't do anything
        // and don't bother to update the element.
        var realGet = methodDescriptor.get;
        methodDescriptor.get = function() {
          if (isFormMethodDialog(this)) {
            return 'dialog';
          }
          return realGet.call(this);
        };
        var realSet = methodDescriptor.set;
        methodDescriptor.set = function(v) {
          if (typeof v === 'string' && v.toLowerCase() === 'dialog') {
            return this.setAttribute('method', v);
          }
          return realSet.call(this, v);
        };
        Object.defineProperty(HTMLFormElement.prototype, 'method', methodDescriptor);
      }
    }

    /**
     * Global 'click' handler, to capture the <input type="submit"> or <button> element which has
     * submitted a <form method="dialog">. Needed as Safari and others don't report this inside
     * document.activeElement.
     */
    document.addEventListener('click', function(ev) {
      dialogPolyfill.formSubmitter = null;
      dialogPolyfill.useValue = null;
      if (ev.defaultPrevented) { return; }  // e.g. a submit which prevents default submission

      var target = /** @type {Element} */ (ev.target);
      if (!target || !isFormMethodDialog(target.form)) { return; }

      var valid = (target.type === 'submit' && ['button', 'input'].indexOf(target.localName) > -1);
      if (!valid) {
        if (!(target.localName === 'input' && target.type === 'image')) { return; }
        // this is a <input type="image">, which can submit forms
        dialogPolyfill.useValue = ev.offsetX + ',' + ev.offsetY;
      }

      var dialog = findNearestDialog(target);
      if (!dialog) { return; }

      dialogPolyfill.formSubmitter = target;

    }, false);

    /**
     * Replace the native HTMLFormElement.submit() method, as it won't fire the
     * submit event and give us a chance to respond.
     */
    var nativeFormSubmit = HTMLFormElement.prototype.submit;
    var replacementFormSubmit = function () {
      if (!isFormMethodDialog(this)) {
        return nativeFormSubmit.call(this);
      }
      var dialog = findNearestDialog(this);
      dialog && dialog.close();
    };
    HTMLFormElement.prototype.submit = replacementFormSubmit;

    /**
     * Global form 'dialog' method handler. Closes a dialog correctly on submit
     * and possibly sets its return value.
     */
    document.addEventListener('submit', function(ev) {
      if (ev.defaultPrevented) { return; }  // e.g. a submit which prevents default submission

      var form = /** @type {HTMLFormElement} */ (ev.target);
      if (!isFormMethodDialog(form)) { return; }
      ev.preventDefault();

      var dialog = findNearestDialog(form);
      if (!dialog) { return; }

      // Forms can only be submitted via .submit() or a click (?), but anyway: sanity-check that
      // the submitter is correct before using its value as .returnValue.
      var s = dialogPolyfill.formSubmitter;
      if (s && s.form === form) {
        dialog.close(dialogPolyfill.useValue || s.value);
      } else {
        dialog.close();
      }
      dialogPolyfill.formSubmitter = null;

    }, false);
  }

  return dialogPolyfill;

}));

  function makeModal(modal) {
    if (typeof HTMLDialogElement !== 'function') {
  // doesn't support modal element so use polyfill
  dialogPolyfill.registerDialog(modal);
} 
  modal
      .querySelector(".gg-c-modal__close-button")
      .addEventListener("click", function() {
        modal.close();
      });
    modal.addEventListener("close", function() {
      document.body.style.overflow = "";
    });

    modal.addEventListener("click", function(event) {
      if (event.target === modal) {
        modal.close();
      }
    });
  }

  const buttonToShowModal = document.querySelector('[data-target="showModal"]');

  function showModal(modal) {
      makeModal(modal);
      document.body.style.overflow = "hidden";
      modal.showModal();
  }

  buttonToShowModal.addEventListener("click", function() {
     showModal(document.querySelector("dialog"));
    });
</script>