diff --git a/css/page-manager.admin.css b/css/page-manager.admin.css
new file mode 100644
index 0000000..39afd04
--- /dev/null
+++ b/css/page-manager.admin.css
@@ -0,0 +1,114 @@
+/**
+ * @file
+ * Styles for Page Manager admin.
+ */
+
+/* Narrow screens */
+
+.page-manager-wizard-tree,
+.page-manager-wizard-form {
+  box-sizing: border-box;
+}
+
+/**
+ * Wizard actions across the top.
+ */
+.page-manager-wizard-actions {
+  text-align: right; /* LTR */
+}
+.page-manager-wizard-actions ul.inline,
+.page-manager-wizard-actions ul.inline li {
+  display: inline-block;
+  margin: 0;
+}
+.page-manager-wizard-actions ul.inline {
+  border-top: 1px solid black;
+  border-left: 1px solid black;
+}
+.page-manager-wizard-actions ul.inline li {
+  border-right: 1px solid black;
+  padding: .5em;
+}
+
+/**
+ * The tree of wizard steps.
+ */
+.page-manager-wizard-tree ul {
+  margin: 0;
+  padding: 0;
+  list-style: none;
+}
+.page-manager-wizard-tree ul > li > ul {
+  margin-left: 1em;
+}
+.page-manager-wizard-tree > ul {
+  border: 1px solid black;
+  padding-bottom: .5em;
+  margin-bottom: 20px;
+}
+.page-manager-wizard-tree li {
+  border-bottom: 1px solid black;
+  padding: .5em;
+  padding-right: 0;
+}
+.page-manager-wizard-tree li:last-child {
+  border-bottom: 0;
+  padding-bottom: 0;
+}
+
+/**
+ * The wizard form.
+ */
+.page-manager-wizard-form {
+  border: 1px solid black;
+  padding: 1em;
+  margin-bottom: 20px;
+}
+
+/* Wide screens */
+@media
+  screen and (min-width: 780px),
+  (orientation: landscape) and (min-device-height: 780px) {
+
+  /**
+   * Overall layout.
+   */
+  .page-manager-wizard-tree {
+    float: left; /* LTR */
+    width: 20%;
+  }
+  .page-manager-wizard-form {
+    float: left; /* LTR */
+    width: 80%;
+  }
+  .page-manager-wizard-form-actions {
+    margin-left: 20%; /* LTR */
+  }
+
+  /**
+   * Make the borders look nice.
+   */
+  .page-manager-wizard-tree > ul {
+    border-right: 0; /* LTR */
+  }
+  .page-manager-wizard-form {
+    min-height: 700px;
+  }
+
+  /**
+   * Right-to-left support.
+   */
+  [dir="rtl"] .page-manager-wizard-tree,
+  [dir="rtl"] .page-manager-wizard-form {
+    float: right;
+  }
+  [dir="rtl"] .page-manager-wizard-form-actions {
+    margin-left: 0;
+    margin-right: 20%;
+  }
+  [dir="rtl"] .page-manager-wizard-tree > ul {
+    border-right: 1px solid black;
+    border-left: 0;
+  }
+}
+
diff --git a/page_manager.libraries.yml b/page_manager.libraries.yml
new file mode 100644
index 0000000..14f4d82
--- /dev/null
+++ b/page_manager.libraries.yml
@@ -0,0 +1,5 @@
+admin:
+  version: VERSION
+  css:
+    layout:
+      css/page-manager.admin.css: {}
diff --git a/page_manager.module b/page_manager.module
index 1031feb..85d5a31 100644
--- a/page_manager.module
+++ b/page_manager.module
@@ -9,6 +9,9 @@
  */
 function page_manager_theme() {
   return [
+    'page_manager_wizard_form' => [
+      'render element' => 'form',
+    ],
     'page_manager_wizard_tree' => [
       'variables' => [
         'wizard' => NULL,
diff --git a/src/Wizard/PageEditWizard.php b/src/Wizard/PageEditWizard.php
index 43c6fba..9730de8 100644
--- a/src/Wizard/PageEditWizard.php
+++ b/src/Wizard/PageEditWizard.php
@@ -132,27 +132,32 @@ class PageEditWizard extends PageWizardBase {
     /** @var $page \Drupal\page_manager\Entity\Page */
     $page = $cached_values['page'];
 
-    // Setup the step rendering theme element.
-    $prefix = [];
-    $prefix['actions'] = [
+    // The page actions.
+    $form['wizard_actions'] = [
       '#theme' => 'links',
       '#links' => [],
+      '#attributes' => [
+        'class' => ['inline'],
+      ]
     ];
     foreach ($this->getPageActionLinks($page) as $action) {
-      $prefix['actions']['#links'][] = $action + [
+      $form['wizard_actions']['#links'][] = $action + [
         'attributes' => [
           'class' => 'use-ajax',
           'data-dialog-type' => 'modal',
         ],
       ];
     }
-    $prefix['tree'] = [
+
+    // The tree of wizard steps.
+    $form['wizard_tree'] = [
       '#theme' => ['page_manager_wizard_tree'],
       '#wizard' => $this,
       '#cached_values' => $form_state->getTemporaryValue('wizard'),
     ];
-    // @todo properly inject the renderer.
-    $form['#prefix'] = \Drupal::service('renderer')->render($prefix);
+
+    $form['#theme'] = 'page_manager_wizard_form';
+    $form['#attached']['library'][] = 'page_manager/admin';
     return $form;
   }
 
diff --git a/templates/page-manager-wizard-form.html.twig b/templates/page-manager-wizard-form.html.twig
new file mode 100644
index 0000000..62fb633
--- /dev/null
+++ b/templates/page-manager-wizard-form.html.twig
@@ -0,0 +1,32 @@
+{#
+/**
+ * @file
+ * Default theme implementation for a 'form' element.
+ *
+ * Available variables
+ * - attributes: A list of HTML attributes for the wrapper element.
+ * - children: The child elements of the form.
+ *
+ * @see template_preprocess_form()
+ *
+ * @ingroup themeable
+ */
+#}
+<div class="page-manager-wizard">
+  <div class="page-manager-wizard-actions">
+    {{ form.wizard_actions }}
+  </div>
+  <div class="page-manager-wizard-main clearfix">
+    <div class="page-manager-wizard-tree">
+      {{ form.wizard_tree }}
+    </div>
+    <div class="page-manager-wizard-form">
+      {{ form|without('wizard_actions', 'wizard_tree', 'actions') }}
+    </div>
+  </div>
+
+  <div class="page-manager-wizard-form-actions">
+    {{ form.actions }}
+  </div>
+</div>
+