diff --git a/spec/pane-container-element-spec.js b/spec/pane-container-element-spec.js
index b50e0c6c1..b4e5f78b7 100644
--- a/spec/pane-container-element-spec.js
+++ b/spec/pane-container-element-spec.js
@@ -42,14 +42,14 @@ describe('PaneContainerElement', function() {
       ]);
 
       paneAxis.removeChild(paneAxis.getChildren()[2]);
-      return expect(childTagNames()).toEqual([
+      expect(childTagNames()).toEqual([
         'atom-pane-axis',
         'atom-pane-resize-handle',
         'atom-pane-axis'
       ]);
     });
 
-    return it('transfers focus to the next pane if a focused pane is removed', function() {
+    it('transfers focus to the next pane if a focused pane is removed', function() {
       const container = new PaneContainer(params);
       const containerElement = container.getElement();
       const leftPane = container.getActivePane();
@@ -62,7 +62,8 @@ describe('PaneContainerElement', function() {
       expect(document.activeElement).toBe(rightPaneElement);
 
       rightPane.destroy();
-      return expect(document.activeElement).toBe(leftPaneElement);
+      expect(containerElement).toHaveClass('panes');
+      expect(document.activeElement).toBe(leftPaneElement);
     });
   });
 
@@ -94,7 +95,7 @@ describe('PaneContainerElement', function() {
       );
       expect(verticalPanes.length).toBe(2);
       expect(verticalPanes[0]).toBe(pane2.getElement());
-      return expect(verticalPanes[1]).toBe(pane3.getElement());
+      expect(verticalPanes[1]).toBe(pane3.getElement());
     }));
 
   describe('when the resize element is dragged ', function() {
@@ -103,9 +104,7 @@ describe('PaneContainerElement', function() {
     beforeEach(function() {
       container = new PaneContainer(params);
       containerElement = container.getElement();
-      return document
-        .querySelector('#jasmine-content')
-        .appendChild(containerElement);
+      document.querySelector('#jasmine-content').appendChild(containerElement);
     });
 
     const dragElementToPosition = function(element, clientX) {
@@ -125,7 +124,7 @@ describe('PaneContainerElement', function() {
         })
       );
 
-      return element.dispatchEvent(
+      element.dispatchEvent(
         new MouseEvent('mouseup', {
           iew: window,
           bubbles: true,
@@ -180,7 +179,7 @@ describe('PaneContainerElement', function() {
       runs(() => expectPaneScale([leftPane, 0.44], [rightPane, 1.55]));
 
       waitsForPromise(() => leftPane.close());
-      return runs(() => expectPaneScale([rightPane, 1]));
+      runs(() => expectPaneScale([rightPane, 1]));
     });
 
     it('splits or closes panes in orthogonal direction that the pane is being dragged', function() {
@@ -206,7 +205,7 @@ describe('PaneContainerElement', function() {
 
       // dynamically close pane, the pane's flexscale will recover to origin value
       waitsForPromise(() => lowerPane.close());
-      return runs(() => expectPaneScale([leftPane, 0.5], [rightPane, 1.5]));
+      runs(() => expectPaneScale([leftPane, 0.5], [rightPane, 1.5]));
     });
 
     it('unsubscribes from mouse events when the pane is detached', function() {
@@ -226,19 +225,19 @@ describe('PaneContainerElement', function() {
 
       waitsFor(() => document.addEventListener.callCount === 2);
 
-      return runs(function() {
+      runs(function() {
         expect(element.resizeStopped.callCount).toBe(0);
         container.destroy();
         expect(element.resizeStopped.callCount).toBe(1);
-        return expect(document.removeEventListener.callCount).toBe(2);
+        expect(document.removeEventListener.callCount).toBe(2);
       });
     });
 
-    return it('does not throw an error when resized to fit content in a detached state', function() {
+    it('does not throw an error when resized to fit content in a detached state', function() {
       container.getActivePane().splitRight();
       const element = getResizeElement(0);
       element.remove();
-      return expect(() => element.resizeToFitContent()).not.toThrow();
+      expect(() => element.resizeToFitContent()).not.toThrow();
     });
   });
 
@@ -248,7 +247,7 @@ describe('PaneContainerElement', function() {
     beforeEach(function() {
       const container = new PaneContainer(params);
       leftPane = container.getActivePane();
-      return (rightPane = leftPane.splitRight());
+      rightPane = leftPane.splitRight();
     });
 
     describe('when pane:increase-size is triggered', () =>
@@ -262,10 +261,10 @@ describe('PaneContainerElement', function() {
 
         atom.commands.dispatch(rightPane.getElement(), 'pane:increase-size');
         expect(leftPane.getFlexScale()).toBe(1.1);
-        return expect(rightPane.getFlexScale()).toBe(1.1);
+        expect(rightPane.getFlexScale()).toBe(1.1);
       }));
 
-    return describe('when pane:decrease-size is triggered', () =>
+    describe('when pane:decrease-size is triggered', () =>
       it('decreases the size of the pane', function() {
         expect(leftPane.getFlexScale()).toBe(1);
         expect(rightPane.getFlexScale()).toBe(1);
@@ -276,16 +275,16 @@ describe('PaneContainerElement', function() {
 
         atom.commands.dispatch(rightPane.getElement(), 'pane:decrease-size');
         expect(leftPane.getFlexScale()).toBe(1 / 1.1);
-        return expect(rightPane.getFlexScale()).toBe(1 / 1.1);
+        expect(rightPane.getFlexScale()).toBe(1 / 1.1);
       }));
   });
 
-  return describe('when only a single pane is present', function() {
+  describe('when only a single pane is present', function() {
     let [singlePane] = [];
 
     beforeEach(function() {
       const container = new PaneContainer(params);
-      return (singlePane = container.getActivePane());
+      singlePane = container.getActivePane();
     });
 
     describe('when pane:increase-size is triggered', () =>
@@ -296,10 +295,10 @@ describe('PaneContainerElement', function() {
         expect(singlePane.getFlexScale()).toBe(1);
 
         atom.commands.dispatch(singlePane.getElement(), 'pane:increase-size');
-        return expect(singlePane.getFlexScale()).toBe(1);
+        expect(singlePane.getFlexScale()).toBe(1);
       }));
 
-    return describe('when pane:decrease-size is triggered', () =>
+    describe('when pane:decrease-size is triggered', () =>
       it('does not decreases the size of the pane', function() {
         expect(singlePane.getFlexScale()).toBe(1);
 
@@ -307,7 +306,7 @@ describe('PaneContainerElement', function() {
         expect(singlePane.getFlexScale()).toBe(1);
 
         atom.commands.dispatch(singlePane.getElement(), 'pane:decrease-size');
-        return expect(singlePane.getFlexScale()).toBe(1);
+        expect(singlePane.getFlexScale()).toBe(1);
       }));
   });
 });
diff --git a/src/pane-container-element.js b/src/pane-container-element.js
index bff5b29c7..f435ceef5 100644
--- a/src/pane-container-element.js
+++ b/src/pane-container-element.js
@@ -1,9 +1,9 @@
 const { CompositeDisposable } = require('event-kit');
 
 class PaneContainerElement extends HTMLElement {
-  createdCallback() {
+  constructor() {
+    super();
     this.subscriptions = new CompositeDisposable();
-    this.classList.add('panes');
   }
 
   initialize(model, { views }) {
@@ -18,6 +18,10 @@ class PaneContainerElement extends HTMLElement {
     return this;
   }
 
+  connectedCallback() {
+    this.classList.add('panes');
+  }
+
   rootChanged(root) {
     const focusedElement = this.hasFocus() ? document.activeElement : null;
     if (this.firstChild != null) {
@@ -39,6 +43,12 @@ class PaneContainerElement extends HTMLElement {
   }
 }
 
-module.exports = document.registerElement('atom-pane-container', {
-  prototype: PaneContainerElement.prototype
-});
+window.customElements.define('atom-pane-container', PaneContainerElement);
+
+function createPaneContainerElement() {
+  return document.createElement('atom-pane-container');
+}
+
+module.exports = {
+  createPaneContainerElement
+};
diff --git a/src/pane-container.js b/src/pane-container.js
index 4cd76dcda..bc2f2a6f6 100644
--- a/src/pane-container.js
+++ b/src/pane-container.js
@@ -2,7 +2,7 @@ const { find } = require('underscore-plus');
 const { Emitter, CompositeDisposable } = require('event-kit');
 const Pane = require('./pane');
 const ItemRegistry = require('./item-registry');
-const PaneContainerElement = require('./pane-container-element');
+const { createPaneContainerElement } = require('./pane-container-element');
 
 const SERIALIZATION_VERSION = 1;
 const STOPPED_CHANGING_ACTIVE_PANE_ITEM_DELAY = 100;
@@ -44,7 +44,7 @@ module.exports = class PaneContainer {
   getElement() {
     return this.element != null
       ? this.element
-      : (this.element = new PaneContainerElement().initialize(this, {
+      : (this.element = createPaneContainerElement().initialize(this, {
           views: this.viewRegistry
         }));
   }