diff --git a/web/modules/contrib/book/src/BookManager.php b/web/modules/contrib/book/src/BookManager.php
index 56e51cf..deca0e9 100644
--- a/web/modules/contrib/book/src/BookManager.php
+++ b/web/modules/contrib/book/src/BookManager.php
@@ -638,6 +638,13 @@ protected function buildItems(array $tree) {
         $element['in_active_trail'] = TRUE;
       }
 
+      // Set a helper variable to indicate whether the link belongs to
+      // the current page.
+      $element['is_active'] = FALSE;
+      if ($data['link']['is_active']) {
+        $element['is_active'] = TRUE;
+      }
+
       // Allow book-specific theme overrides.
       $element['attributes'] = new Attribute();
       $element['title'] = $data['link']['title'];
@@ -1113,7 +1120,14 @@ protected function buildBookOutlineData(array $links, array $parents = [], $dept
    */
   protected function buildBookOutlineRecursive(&$links, $parents, $depth) {
     $tree = [];
+    $node = \Drupal::routeMatch()->getParameter('node');
+    // The instanceof check doesn't filter out NULLs.
+    if ($node != NULL && !($node instanceof NodeInterface)) {
+      $node = $this->entityTypeManager->getStorage('node')->load($node);
+    }
     while ($item = array_pop($links)) {
+      // Check if item belongs to the current page.
+      $item['is_active'] = ($node && $node->id() == $item['nid']) ? TRUE : FALSE;
       // We need to determine if we're on the path to root so we can later build
       // the correct active trail.
       $item['in_active_trail'] = in_array($item['nid'], $parents);
diff --git a/web/modules/contrib/book/src/Plugin/Block/BookNavigationBlock.php b/web/modules/contrib/book/src/Plugin/Block/BookNavigationBlock.php
index 578ea36..9fe5929 100644
--- a/web/modules/contrib/book/src/Plugin/Block/BookNavigationBlock.php
+++ b/web/modules/contrib/book/src/Plugin/Block/BookNavigationBlock.php
@@ -142,6 +142,7 @@ public function build() {
           // Since we know we will only display a link to the top node, there
           // is no reason to run an additional menu tree query for each book.
           $book['in_active_trail'] = FALSE;
+          $book['is_active'] = FALSE;
           // Check whether user can access the book link.
           $book_node = $this->nodeStorage->load($book['nid']);
           $book['access'] = $book_node->access('view');
diff --git a/web/modules/contrib/book/templates/book-tree.html.twig b/web/modules/contrib/book/templates/book-tree.html.twig
index 3d3069c..39b88b2 100644
--- a/web/modules/contrib/book/templates/book-tree.html.twig
+++ b/web/modules/contrib/book/templates/book-tree.html.twig
@@ -16,6 +16,7 @@
  *   - is_collapsed: TRUE if the link has children within the current book tree
  *     that are not currently visible.
  *   - in_active_trail: TRUE if the link is in the active trail.
+ *   - is_active: TRUE if the link is for the current page.
  *
  * @ingroup themeable
  */