diff --git a/manual/edit.rst b/manual/edit.rst
index 11adc43dd7..661d4943e7 100644
--- a/manual/edit.rst
+++ b/manual/edit.rst
@@ -375,6 +375,21 @@ Note that the algorithm can sometimes generate incorrect results, especially
 when single quotes at the start of contractions are involved. Accessed via
 :guilabel:`Tools->Smarten punctuation`.
 
+Transforming CSS properties
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Create rules to transform the stying of the book. For example, create a rule
+to convert all red text to green or to double the font size of all text in the
+book or make text of a certain font family italic, etc.
+
+Creating the rules is simple, the rules follow a natural language format, that
+looks like:
+
+ * If the property *color* is *red* *change* it to *green*
+ * If the property *font-size* is *any value* *multiply* the value by *2*
+
+Accessed via :guilabel:`Tools->Transform styles`.
+
 Removing unused CSS rules
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/src/calibre/gui2/tweak_book/boss.py b/src/calibre/gui2/tweak_book/boss.py
index 0941cbbb2c..a4fb5fcd95 100644
--- a/src/calibre/gui2/tweak_book/boss.py
+++ b/src/calibre/gui2/tweak_book/boss.py
@@ -50,6 +50,7 @@ from calibre.utils.config import JSONConfig
 from calibre.utils.icu import numeric_sort_key
 
 _diff_dialogs = []
+last_used_transform_rules = []
 
 def get_container(*args, **kwargs):
     kwargs['tweak_mode'] = True
@@ -543,6 +544,34 @@ class Boss(QObject):
             self.rewind_savepoint()
         show_report(changed, self.current_metadata.title, report, parent or self.gui, self.show_current_diff)
 
+    def transform_styles(self):
+        global last_used_transform_rules
+        if not self.ensure_book(_('You must first open a book in order to transform styles.')):
+            return
+        from calibre.gui2.css_transform_rules import RulesDialog
+        from calibre.ebooks.css_transform_rules import transform_container
+        d = RulesDialog(self.gui)
+        d.rules = last_used_transform_rules
+        ret = d.exec_()
+        last_used_transform_rules = d.rules
+        if ret != d.Accepted:
+            return
+        with BusyCursor():
+            self.add_savepoint(_('Before style transformation'))
+            try:
+                changed = transform_container(current_container(), last_used_transform_rules)
+            except:
+                self.rewind_savepoint()
+                raise
+            if changed:
+                self.apply_container_update_to_gui()
+        if not changed:
+            self.rewind_savepoint()
+            info_dialog(self.gui, _('No changes'), _(
+                'No styles were changed.'), show=True)
+            return
+        self.show_current_diff()
+
     def manage_fonts(self):
         self.commit_all_editors_to_container()
         self.gui.manage_fonts.display()
diff --git a/src/calibre/gui2/tweak_book/ui.py b/src/calibre/gui2/tweak_book/ui.py
index 15d2339351..ec8b4fab3e 100644
--- a/src/calibre/gui2/tweak_book/ui.py
+++ b/src/calibre/gui2/tweak_book/ui.py
@@ -392,6 +392,8 @@ class Main(MainWindow):
             'Check external links in the book'))
         self.action_compress_images = treg('compress-image.png', _('Compress &images losslessly'), self.boss.compress_images, 'compress-images', (), _(
             'Compress images losslessly'))
+        self.action_transform_styles = treg('wizard.png', _('Transform &styles'), self.boss.transform_styles, 'transform-styles', (), _(
+            'Transform styles used in the book'))
 
         def ereg(icon, text, target, sid, keys, description):
             return reg(icon, text, partial(self.boss.editor_action, target), sid, keys, description)
@@ -543,6 +545,7 @@ class Main(MainWindow):
         e.addAction(self.action_compress_images)
         e.addAction(self.action_smarten_punctuation)
         e.addAction(self.action_remove_unused_css)
+        e.addAction(self.action_transform_styles)
         e.addAction(self.action_fix_html_all)
         e.addAction(self.action_pretty_all)
         e.addAction(self.action_rationalize_folders)