diff --git a/modules/book/book-rtl.css b/modules/book/book-rtl.css
deleted file mode 100644
index f3a84c2..0000000
--- a/modules/book/book-rtl.css
+++ /dev/null
@@ -1,11 +0,0 @@
-
-.book-navigation .menu {
-  padding: 1em 3em 0 0;
-}
-
-.book-navigation .page-previous {
-  float: right;
-}
-.book-navigation .page-up {
-  float: right;
-}
diff --git a/modules/book/book.base.css b/modules/book/book.base.css
new file mode 100644
index 0000000..e76cb3c
--- /dev/null
+++ b/modules/book/book.base.css
@@ -0,0 +1,12 @@
+
+/**
+ * @file
+ * Generic base styles for book module.
+ */
+
+/**
+ * Book outline on book edit form.
+ */
+.js #edit-book-pick-book {
+  display: none;
+}
diff --git a/modules/book/book.css b/modules/book/book.css
deleted file mode 100644
index 3348c0f..0000000
--- a/modules/book/book.css
+++ /dev/null
@@ -1,51 +0,0 @@
-
-.book-navigation .menu {
-  border-top: 1px solid #888;
-  padding: 1em 0 0 3em; /* LTR */
-}
-.book-navigation .page-links {
-  border-top: 1px solid #888;
-  border-bottom: 1px solid #888;
-  text-align: center;
-  padding: 0.5em;
-}
-.book-navigation .page-previous {
-  text-align: left;
-  width: 42%;
-  display: block;
-  float: left; /* LTR */
-}
-.book-navigation .page-up {
-  margin: 0 5%;
-  width: 4%;
-  display: block;
-  float: left; /* LTR */
-}
-.book-navigation .page-next {
-  text-align: right;
-  width: 42%;
-  display: block;
-  float: right;
-}
-.book-outline-form .form-item {
-  margin-top: 0;
-  margin-bottom: 0;
-}
-html.js #edit-book-pick-book {
-  display: none;
-}
-.form-item-book-bid .description {
-  clear: both;
-}
-#book-admin-edit select {
-  margin-right: 24px;
-}
-#book-admin-edit select.progress-disabled {
-  margin-right: 0;
-}
-#book-admin-edit tr.ajax-new-content {
-  background-color: #ffd;
-}
-#book-admin-edit .form-item {
-  float: left;
-}
diff --git a/modules/book/book.info b/modules/book/book.info
index 0f4d2b1..15984ad 100644
--- a/modules/book/book.info
+++ b/modules/book/book.info
@@ -5,4 +5,4 @@ version = VERSION
 core = 8.x
 files[] = book.test
 configure = admin/content/book/settings
-stylesheets[all][] = book.css
+stylesheets[all][] = book.theme.css
diff --git a/modules/book/book.module b/modules/book/book.module
index fee2467..a4c64eb 100644
--- a/modules/book/book.module
+++ b/modules/book/book.module
@@ -408,6 +408,9 @@ function book_form_node_form_alter(&$form, &$form_state, $form_id) {
       '#value' => t('Change book (update list of parents)'),
       '#submit' => array('book_pick_book_nojs_submit'),
       '#weight' => 20,
+      '#attached' => array(
+        'css' => array(drupal_get_path('module', 'book') . '/book.base.css'),
+      ),
     );
   }
 }
diff --git a/modules/book/book.theme-rtl.css b/modules/book/book.theme-rtl.css
new file mode 100644
index 0000000..e7ce8cb
--- /dev/null
+++ b/modules/book/book.theme-rtl.css
@@ -0,0 +1,16 @@
+
+/**
+ * @file
+ * RTL styling for the book module.
+ */
+
+/**
+ * Book navigation.
+ */
+.book-navigation .menu {
+  padding: 1em 3em 0 0;
+}
+.book-navigation .page-previous,
+.book-navigation .page-up {
+  float: right;
+}
diff --git a/modules/book/book.theme.css b/modules/book/book.theme.css
new file mode 100644
index 0000000..c66afa1
--- /dev/null
+++ b/modules/book/book.theme.css
@@ -0,0 +1,37 @@
+
+/**
+ * @file
+ * Styling for the book module.
+ */
+
+/**
+ * Book navigation.
+ */
+.book-navigation .menu {
+  border-top: 1px solid #888;
+  padding: 1em 0 0 3em; /* LTR */
+}
+.book-navigation .page-links {
+  border-bottom: 1px solid #888;
+  border-top: 1px solid #888;
+  padding: 0.5em;
+  text-align: center;
+}
+.book-navigation .page-previous {
+  display: block;
+  float: left; /* LTR */
+  text-align: left;
+  width: 42%;
+}
+.book-navigation .page-up {
+  display: block;
+  float: left; /* LTR */
+  margin: 0 5%;
+  width: 4%;
+}
+.book-navigation .page-next {
+  display: block;
+  float: right;
+  text-align: right;
+  width: 42%;
+}