diff --git a/.hgignore b/.hgignore
--- a/.hgignore
+++ b/.hgignore
@@ -23,6 +23,7 @@ syntax: regexp
 ^\.pydevproject$
 ^\.coverage$
 ^kallithea/public/css/style\.css$
+^theme\.less$
 ^kallithea\.db$
 ^test\.db$
 ^Kallithea\.egg-info$
diff --git a/docs/usage/customization.rst b/docs/usage/customization.rst
--- a/docs/usage/customization.rst
+++ b/docs/usage/customization.rst
@@ -18,6 +18,29 @@ you can enter HTML code (possibly with J
 block*.
 
 
+Style sheet customization with Less
+-----------------------------------
+
+Kallithea uses `Bootstrap 3`_ and Less_ for its style definitions. If you want
+to make some customizations, we recommend to do so by creating a ``theme.less``
+file. When you create a file named ``theme.less`` in the Kallithea root
+directory, you can use this file to override the default style. For example,
+you can use this to override ``@kallithea-theme-main-color``,
+``@kallithea-logo-url`` or other `Bootstrap variables`_.
+
+After creating the ``theme.less`` file, you need to regenerate the CSS files.
+Install npm for your platform and run::
+
+    npm install
+    npm run less
+
+in the Kallithea root directory.
+
+.. _bootstrap 3: https://getbootstrap.com/docs/3.3/
+.. _bootstrap variables: https://getbootstrap.com/docs/3.3/customize/#less-variables
+.. _less: http://lesscss.org/
+
+
 Behavioral customization: rcextensions
 --------------------------------------
 
diff --git a/kallithea/public/less/main.less b/kallithea/public/less/main.less
--- a/kallithea/public/less/main.less
+++ b/kallithea/public/less/main.less
@@ -23,3 +23,6 @@
 @import "kallithea-select2.less";
 @import "kallithea-diff.less";
 @import "style.less";
+
+/* finally, import the optional theme file with local customizations */
+@import (optional) "theme.less";