diff --git a/core/modules/layout_builder/css/layout-builder.css b/core/modules/layout_builder/css/layout-builder.css
index 4c547e9..11d8c55 100644
--- a/core/modules/layout_builder/css/layout-builder.css
+++ b/core/modules/layout_builder/css/layout-builder.css
@@ -40,20 +40,12 @@
   background-image: url(../../../misc/icons/787878/ex.svg);
 }
 
-#drupal-off-canvas details.layout-selection {
-  background-color: transparent;
-}
-
-#drupal-off-canvas details.layout-selection summary {
-  margin-bottom: 1em;
-}
-
-#drupal-off-canvas details.layout-selection li {
+#drupal-off-canvas .layout-selection li {
   display: block;
   padding-bottom: 1em;
 }
 
-#drupal-off-canvas details.layout-selection li a {
+#drupal-off-canvas .layout-selection li a {
   display: block;
   padding-top: 0.55em;
 }
diff --git a/core/modules/layout_builder/js/layout-builder.es6.js b/core/modules/layout_builder/js/layout-builder.es6.js
index 150f9a6..391e462 100644
--- a/core/modules/layout_builder/js/layout-builder.es6.js
+++ b/core/modules/layout_builder/js/layout-builder.es6.js
@@ -14,21 +14,20 @@
          *   An object containing information about the item being sorted.
          */
         update(event, ui) {
-          const data = {
-            region_to: $(this).data('region'),
-            block_uuid: ui.item.data('layout-block-uuid'),
-            delta_to: ui.item.closest('[data-layout-delta]').data('layout-delta'),
-            preceding_block_uuid: ui.item.prev('[data-layout-block-uuid]').data('layout-block-uuid'),
-          };
-
           // Only process if the item was moved from one region to another.
           if (ui.sender) {
-            data.region_from = ui.sender.data('region');
-            data.delta_from = ui.sender.closest('[data-layout-delta]').data('layout-delta');
-
             ajax({
-              url: ui.item.closest('[data-layout-update-url]').data('layout-update-url'),
-              submit: data,
+              url: [
+                ui.item.closest('[data-layout-update-url]').data('layout-update-url'),
+                ui.sender.closest('[data-layout-delta]').data('layout-delta'),
+                ui.item.closest('[data-layout-delta]').data('layout-delta'),
+                ui.sender.data('region'),
+                $(this).data('region'),
+                ui.item.data('layout-block-uuid'),
+                ui.item.prev('[data-layout-block-uuid]').data('layout-block-uuid'),
+              ]
+              .filter(element => element !== undefined)
+              .join('/'),
             }).execute();
           }
         },
diff --git a/core/modules/layout_builder/js/layout-builder.js b/core/modules/layout_builder/js/layout-builder.js
index e9f6558..d4dadc8 100644
--- a/core/modules/layout_builder/js/layout-builder.js
+++ b/core/modules/layout_builder/js/layout-builder.js
@@ -16,20 +16,11 @@
         connectWith: '.layout-builder--layout__region',
 
         update: function update(event, ui) {
-          var data = {
-            region_to: $(this).data('region'),
-            block_uuid: ui.item.data('layout-block-uuid'),
-            delta_to: ui.item.closest('[data-layout-delta]').data('layout-delta'),
-            preceding_block_uuid: ui.item.prev('[data-layout-block-uuid]').data('layout-block-uuid')
-          };
-
           if (ui.sender) {
-            data.region_from = ui.sender.data('region');
-            data.delta_from = ui.sender.closest('[data-layout-delta]').data('layout-delta');
-
             ajax({
-              url: ui.item.closest('[data-layout-update-url]').data('layout-update-url'),
-              submit: data
+              url: [ui.item.closest('[data-layout-update-url]').data('layout-update-url'), ui.sender.closest('[data-layout-delta]').data('layout-delta'), ui.item.closest('[data-layout-delta]').data('layout-delta'), ui.sender.data('region'), $(this).data('region'), ui.item.data('layout-block-uuid'), ui.item.prev('[data-layout-block-uuid]').data('layout-block-uuid')].filter(function (element) {
+                return element !== undefined;
+              }).join('/')
             }).execute();
           }
         }
diff --git a/core/modules/layout_builder/layout_builder.module b/core/modules/layout_builder/layout_builder.module
index 12545bc..e8d8a11 100644
--- a/core/modules/layout_builder/layout_builder.module
+++ b/core/modules/layout_builder/layout_builder.module
@@ -44,7 +44,7 @@ function layout_builder_form_entity_view_display_edit_form_alter(&$form, FormSta
     '#tree' => TRUE,
   ];
   // @todo Unchecking this box is a destructive action, this should be made
-  //   clear to the user.
+  //   clear to the user in https://www.drupal.org/node/2914484.
   $form['layout']['allow_custom'] = [
     '#type' => 'checkbox',
     '#title' => t('Allow each @entity to have its layout customized.', [
diff --git a/core/modules/layout_builder/layout_builder.permissions.yml b/core/modules/layout_builder/layout_builder.permissions.yml
index 1fca7af..00aac63 100644
--- a/core/modules/layout_builder/layout_builder.permissions.yml
+++ b/core/modules/layout_builder/layout_builder.permissions.yml
@@ -1,4 +1,5 @@
-# @todo Expand permissions to be more granular.
+# @todo Expand permissions to be more granular in
+#   https://www.drupal.org/node/2914486.
 configure any layout:
   title: 'Configure any layout'
   restrict access: true
diff --git a/core/modules/layout_builder/layout_builder.routing.yml b/core/modules/layout_builder/layout_builder.routing.yml
index 78e7410..27a234a 100644
--- a/core/modules/layout_builder/layout_builder.routing.yml
+++ b/core/modules/layout_builder/layout_builder.routing.yml
@@ -107,10 +107,15 @@ layout_builder.remove_block:
         layout_builder_tempstore: TRUE
 
 layout_builder.move_block:
-  path: '/layout_builder/move/block/{entity_type_id}/{entity}'
+  path: '/layout_builder/move/block/{entity_type_id}/{entity}/{delta_from}/{delta_to}/{region_from}/{region_to}/{block_uuid}/{preceding_block_uuid}'
   defaults:
     _controller: '\Drupal\layout_builder\Controller\MoveBlockController::build'
-  methods: [POST]
+    delta_from: null
+    delta_to: null
+    region_from: null
+    region_to: null
+    block_uuid: null
+    preceding_block_uuid: null
   requirements:
     _permission: 'configure any layout'
   options:
diff --git a/core/modules/layout_builder/src/Access/LayoutSectionAccessCheck.php b/core/modules/layout_builder/src/Access/LayoutSectionAccessCheck.php
index d756ca3..e3833cc 100644
--- a/core/modules/layout_builder/src/Access/LayoutSectionAccessCheck.php
+++ b/core/modules/layout_builder/src/Access/LayoutSectionAccessCheck.php
@@ -43,7 +43,7 @@ public function __construct(EntityTypeManagerInterface $entity_type_manager) {
    *   The access result.
    */
   public function access(RouteMatchInterface $route_match, AccountInterface $account) {
-    // Attempt to retrive the generic 'entity' parameter, otherwise look up the
+    // Attempt to retrieve the generic 'entity' parameter, otherwise look up the
     // specific entity via the entity type ID.
     $entity = $route_match->getParameter('entity') ?: $route_match->getParameter($route_match->getParameter('entity_type_id'));
 
diff --git a/core/modules/layout_builder/src/Controller/AddSectionController.php b/core/modules/layout_builder/src/Controller/AddSectionController.php
index 5f6b9ce..117bb7f6 100644
--- a/core/modules/layout_builder/src/Controller/AddSectionController.php
+++ b/core/modules/layout_builder/src/Controller/AddSectionController.php
@@ -12,7 +12,7 @@
 use Symfony\Component\HttpFoundation\RequestStack;
 
 /**
- * @todo.
+ * Defines a controller to add a new section.
  */
 class AddSectionController implements ContainerInjectionInterface {
 
diff --git a/core/modules/layout_builder/src/Controller/ChooseBlockController.php b/core/modules/layout_builder/src/Controller/ChooseBlockController.php
index 3d2ff8b..5ff7d4e 100644
--- a/core/modules/layout_builder/src/Controller/ChooseBlockController.php
+++ b/core/modules/layout_builder/src/Controller/ChooseBlockController.php
@@ -10,7 +10,7 @@
 use Symfony\Component\HttpFoundation\RequestStack;
 
 /**
- * @todo.
+ * Defines a controller to choose a new block.
  */
 class ChooseBlockController implements ContainerInjectionInterface {
 
diff --git a/core/modules/layout_builder/src/Controller/ChooseSectionController.php b/core/modules/layout_builder/src/Controller/ChooseSectionController.php
index 7055f6e..0ecd28b 100644
--- a/core/modules/layout_builder/src/Controller/ChooseSectionController.php
+++ b/core/modules/layout_builder/src/Controller/ChooseSectionController.php
@@ -12,7 +12,7 @@
 use Symfony\Component\HttpFoundation\RequestStack;
 
 /**
- * @todo.
+ * Defines a controller to choose a new section.
  */
 class ChooseSectionController implements ContainerInjectionInterface {
 
@@ -61,7 +61,8 @@ public static function create(ContainerInterface $container) {
    *   The render array.
    */
   public function build(EntityInterface $entity, $delta) {
-    $output = [];
+    $output['#title'] = $this->t('Choose a layout');
+
     $items = [];
     foreach ($this->layoutManager->getDefinitions() as $plugin_id => $definition) {
       $layout = $this->layoutManager->createInstance($plugin_id);
@@ -91,25 +92,14 @@ public function build(EntityInterface $entity, $delta) {
       }
       $items[] = $item;
     }
-    // @todo Look into removing this details wrapper, or rewording the title.
     $output['layouts'] = [
-      '#type' => 'details',
-      '#title' => $this->t('Basic Layouts'),
-      '#open' => TRUE,
+      '#theme' => 'item_list',
+      '#items' => $items,
       '#attributes' => [
         'class' => [
           'layout-selection',
         ],
       ],
-      'list' => [
-        '#theme' => 'item_list',
-        '#items' => $items,
-        '#attributes' => [
-          'class' => [
-            'layout-list',
-          ],
-        ],
-      ],
     ];
 
     return $output;
diff --git a/core/modules/layout_builder/src/Controller/LayoutBuilderController.php b/core/modules/layout_builder/src/Controller/LayoutBuilderController.php
index 0195599..abf35e1 100644
--- a/core/modules/layout_builder/src/Controller/LayoutBuilderController.php
+++ b/core/modules/layout_builder/src/Controller/LayoutBuilderController.php
@@ -16,7 +16,7 @@
 use Symfony\Component\HttpFoundation\RedirectResponse;
 
 /**
- * @todo.
+ * Defines a controller to provide the Layout Builder admin UI.
  */
 class LayoutBuilderController implements ContainerInjectionInterface {
 
@@ -225,6 +225,7 @@ protected function buildAdministrativeSection(LayoutSectionItemInterface $item,
       ];
       $build[$region]['layout_builder_add_block']['#type'] = 'container';
       $build[$region]['layout_builder_add_block']['#attributes'] = ['class' => ['add-block']];
+      $build[$region]['layout_builder_add_block']['#weight'] = -1000;
       $build[$region]['#attributes']['data-region'] = $region;
       $build[$region]['#attributes']['class'][] = 'layout-builder--layout__region';
     }
diff --git a/core/modules/layout_builder/src/Controller/MoveBlockController.php b/core/modules/layout_builder/src/Controller/MoveBlockController.php
index b1b771d..33e7570 100644
--- a/core/modules/layout_builder/src/Controller/MoveBlockController.php
+++ b/core/modules/layout_builder/src/Controller/MoveBlockController.php
@@ -11,7 +11,7 @@
 use Symfony\Component\HttpFoundation\RequestStack;
 
 /**
- * @todo.
+ * Defines a controller to move a block.
  */
 class MoveBlockController implements ContainerInjectionInterface {
 
@@ -63,27 +63,29 @@ public static function create(ContainerInterface $container) {
    * @return \Drupal\Core\Ajax\AjaxResponse
    *   An AJAX response.
    */
-  public function build(EntityInterface $entity, Request $request) {
-    // @todo Either enforce the presence of each part of $data, or convert this
-    //   to use URL parameters.
-    $data = $request->request->all();
-
+  public function build(EntityInterface $entity, Request $request, $delta_from, $delta_to, $region_from, $region_to, $block_uuid, $preceding_block_uuid = NULL) {
     /** @var \Drupal\layout_builder\LayoutSectionItemInterface $field */
-    $field = $entity->layout_builder__layout->get($data['delta_from']);
+    $field = $entity->layout_builder__layout->get($delta_from);
     $values = $field->section;
 
-    $region_from = $data['region_from'];
-    $region_to = $data['region_to'];
-    $block_uuid = $data['block_uuid'];
     $configuration = $values[$region_from][$block_uuid];
     unset($values[$region_from][$block_uuid]);
     $field->section = array_filter($values);
 
     /** @var \Drupal\layout_builder\LayoutSectionItemInterface $field */
-    $field = $entity->layout_builder__layout->get($data['delta_to']);
+    $field = $entity->layout_builder__layout->get($delta_to);
     $values = $field->section;
-    if (isset($data['preceding_block_uuid'])) {
-      $slice_id = array_search($data['preceding_block_uuid'], array_keys($values[$region_to]));
+
+    if (isset($preceding_block_uuid)) {
+      if (!isset($values[$region_to])) {
+        throw new \InvalidArgumentException('Invalid region');
+      }
+
+      $slice_id = array_search($preceding_block_uuid, array_keys($values[$region_to]));
+      if ($slice_id === FALSE) {
+        throw new \InvalidArgumentException('Invalid preceeding block UUID');
+      }
+
       $before = array_slice($values[$region_to], 0, $slice_id + 1);
       $after = array_slice($values[$region_to], $slice_id + 1);
       $values[$region_to] = array_merge($before, [$block_uuid => $configuration], $after);
diff --git a/core/modules/layout_builder/src/Plugin/Field/FieldType/LayoutSectionItem.php b/core/modules/layout_builder/src/Plugin/Field/FieldType/LayoutSectionItem.php
index ab7aae7..136073b 100644
--- a/core/modules/layout_builder/src/Plugin/Field/FieldType/LayoutSectionItem.php
+++ b/core/modules/layout_builder/src/Plugin/Field/FieldType/LayoutSectionItem.php
@@ -78,13 +78,13 @@ public static function schema(FieldStorageDefinitionInterface $field_definition)
         'layout_settings' => [
           'type' => 'blob',
           'size' => 'normal',
-          // @todo Is this okay?
+          // @todo Address in https://www.drupal.org/node/2914503.
           'serialize' => TRUE,
         ],
         'section' => [
           'type' => 'blob',
           'size' => 'normal',
-          // @todo Is this okay?
+          // @todo Address in https://www.drupal.org/node/2914503.
           'serialize' => TRUE,
         ],
       ],
diff --git a/core/modules/layout_builder/src/Plugin/Menu/LayoutBuilderLocalTask.php b/core/modules/layout_builder/src/Plugin/Menu/LayoutBuilderLocalTask.php
index d2feff1..cddbdde 100644
--- a/core/modules/layout_builder/src/Plugin/Menu/LayoutBuilderLocalTask.php
+++ b/core/modules/layout_builder/src/Plugin/Menu/LayoutBuilderLocalTask.php
@@ -16,9 +16,7 @@ class LayoutBuilderLocalTask extends LocalTaskDefault {
   public function getRouteParameters(RouteMatchInterface $route_match) {
     $parameters = parent::getRouteParameters($route_match);
 
-    // @todo This assumes that the route match contains a valid entity,
-    //   investigate whether that assumption is safe, or if this code is even
-    //   needed.
+    // @todo Revisit this code once https://www.drupal.org/node/2912363 is in.
     $parameters['entity'] = $route_match->getParameter('entity');
     return $parameters;
   }
diff --git a/core/modules/layout_builder/src/Routing/LayoutBuilderRouteEnhancer.php b/core/modules/layout_builder/src/Routing/LayoutBuilderRouteEnhancer.php
index 0faca8f..840c670 100644
--- a/core/modules/layout_builder/src/Routing/LayoutBuilderRouteEnhancer.php
+++ b/core/modules/layout_builder/src/Routing/LayoutBuilderRouteEnhancer.php
@@ -16,16 +16,15 @@ class LayoutBuilderRouteEnhancer implements RouteEnhancerInterface {
    * {@inheritdoc}
    */
   public function applies(Route $route) {
-    // Find layout builder routes that override existing paths.
-    return $route->hasOption('_layout_builder');
+    return $route->getOption('_layout_builder') && $route->getDefault('entity_type_id');
   }
 
   /**
    * {@inheritdoc}
    */
   public function enhance(array $defaults, Request $request) {
-    if (!isset($defaults['entity_type_id'])) {
-      throw new \RuntimeException(sprintf('Failed to find the entity type ID in route named %s', $defaults[RouteObjectInterface::ROUTE_NAME]));
+    if (!isset($defaults[$defaults['entity_type_id']])) {
+      throw new \RuntimeException(sprintf('Failed to find the "%s" entity in route named %s', $defaults['entity_type_id'], $defaults[RouteObjectInterface::ROUTE_NAME]));
     }
 
     // Copy the entity by reference so that any changes are reflected.
diff --git a/core/modules/layout_builder/tests/src/Unit/LayoutBuilderRouteEnhancerTest.php b/core/modules/layout_builder/tests/src/Unit/LayoutBuilderRouteEnhancerTest.php
new file mode 100644
index 0000000..6e449c6
--- /dev/null
+++ b/core/modules/layout_builder/tests/src/Unit/LayoutBuilderRouteEnhancerTest.php
@@ -0,0 +1,133 @@
+<?php
+
+namespace Drupal\Tests\layout_builder\Unit;
+
+use Drupal\layout_builder\Routing\LayoutBuilderRouteEnhancer;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Cmf\Component\Routing\RouteObjectInterface;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\Routing\Route;
+
+/**
+ * @coversDefaultClass \Drupal\layout_builder\Routing\LayoutBuilderRouteEnhancer
+ * @group layout_builder
+ */
+class LayoutBuilderRouteEnhancerTest extends UnitTestCase {
+
+  /**
+   * @covers ::applies
+   * @dataProvider providerTestApplies
+   */
+  public function testApplies($defaults, $options, $expected) {
+    $route_enhancer = new LayoutBuilderRouteEnhancer();
+    $route = new Route('/some/path', $defaults, [], $options);
+
+    $result = $route_enhancer->applies($route);
+    $this->assertSame($expected, $result);
+  }
+
+  /**
+   * Provides test data for ::testApplies().
+   */
+  public function providerTestApplies() {
+    $data = [];
+    $data['layout_builder_true'] = [
+      ['entity_type_id' => 'the_entity_type'],
+      ['_layout_builder' => TRUE],
+      TRUE,
+    ];
+    $data['layout_builder_false'] = [
+      ['entity_type_id' => 'the_entity_type'],
+      ['_layout_builder' => FALSE],
+      FALSE,
+    ];
+    $data['layout_builder_null'] = [
+      ['entity_type_id' => 'the_entity_type'],
+      ['_layout_builder' => NULL],
+      FALSE,
+    ];
+    $data['entity_type_id_empty'] = [
+      ['entity_type_id' => ''],
+      ['_layout_builder' => TRUE],
+      FALSE,
+    ];
+    $data['no_entity_type_id'] = [
+      [],
+      ['_layout_builder' => TRUE],
+      FALSE,
+    ];
+    $data['no_layout_builder'] = [
+      ['entity_type_id' => 'the_entity_type'],
+      [],
+      FALSE,
+    ];
+    $data['empty'] = [
+      [],
+      [],
+      FALSE,
+    ];
+    return $data;
+  }
+
+  /**
+   * @covers ::enhance
+   */
+  public function testEnhanceValidDefaults() {
+    $route_enhancer = new LayoutBuilderRouteEnhancer();
+    $object = new \stdClass();
+    $defaults = [
+      'entity_type_id' => 'the_entity_type',
+      'the_entity_type' => $object,
+    ];
+    // Ensure that the 'entity' key now contains the value stored for a given
+    // entity type.
+    $expected = [
+      'entity_type_id' => 'the_entity_type',
+      'the_entity_type' => $object,
+      'entity' => $object,
+    ];
+
+    $result = $route_enhancer->enhance($defaults, new Request());
+    $this->assertEquals($expected, $result);
+    $this->assertSame($object, $result['entity']);
+
+    // Modifying the original value updates the 'entity' copy.
+    $result['the_entity_type'] = 'something else';
+    $this->assertSame('something else', $result['entity']);
+  }
+
+  /**
+   * @covers ::enhance
+   */
+  public function testEnhanceMissingEntity() {
+    $route_enhancer = new LayoutBuilderRouteEnhancer();
+    $defaults = [
+      RouteObjectInterface::ROUTE_NAME => 'the_route',
+      'entity_type_id' => 'the_entity_type',
+    ];
+    $this->setExpectedException(\RuntimeException::class, 'Failed to find the "the_entity_type" entity in route named the_route');
+    $route_enhancer->enhance($defaults, new Request());
+  }
+
+  /**
+   * Provides test data for ::testEnhanceException().
+   */
+  public function providerTestEnhanceException() {
+    $data = [];
+    $data['missing_entity'] = [
+      [
+        RouteObjectInterface::ROUTE_NAME => 'the_route',
+        'entity_type_id' => 'the_entity_type',
+      ],
+      'Failed to find the "the_entity_type" entity in route named the_route',
+    ];
+    $data['missing_entity_type_id'] = [
+      [
+        RouteObjectInterface::ROUTE_NAME => 'the_route',
+      ],
+      'Failed to find an entity type ID in route named the_route',
+    ];
+    return $data;
+  }
+
+}
diff --git a/core/modules/settings_tray/css/off-canvas.reset.css b/core/modules/settings_tray/css/off-canvas.reset.css
index 796da64..ee12792 100644
--- a/core/modules/settings_tray/css/off-canvas.reset.css
+++ b/core/modules/settings_tray/css/off-canvas.reset.css
@@ -13,8 +13,7 @@
 #drupal-off-canvas *:not(svg *),
 #drupal-off-canvas *:after,
 #drupal-off-canvas *:before {
-  /* @todo This breaks SVGs, fix in https://www.drupal.org/node/2907420. */
-  /*all: initial;*/
+  all: initial;
   box-sizing: border-box;
   text-shadow: none;
   -webkit-font-smoothing: antialiased;