diff --git a/README.md b/README.md
index ed9248a0..0624123c 100644
--- a/README.md
+++ b/README.md
@@ -536,6 +536,14 @@ Note that filenames on windows must not contain any of the following characters
 
 Gollum optionally takes a `--config file`. See [config.rb](https://github.com/github/gollum/blob/master/config.rb) for an example.
 
+## CUSTOM CSS
+
+The `--css` flag will inject `custom.css` from the root of your git repository into each page. Here's an example of floating the sidebar to the left.
+
+```css
+#wiki-rightbar { float: left !important; }
+```
+
 ## CONTRIBUTE
 
 If you'd like to hack on Gollum, start by forking my repo on GitHub:
diff --git a/bin/gollum b/bin/gollum
index 3f98a988..2ea1aa17 100755
--- a/bin/gollum
+++ b/bin/gollum
@@ -45,6 +45,10 @@ opts = OptionParser.new do |opts|
     options['irb'] = true
   end
 
+  opts.on("--css", "Inject custom css. Uses custom.css from root repository") do
+    wiki_options[:css] = true
+  end
+
   opts.on("--page-file-dir [PATH]", "Specify the sub directory for all page files (default: repository root).") do |path|
     wiki_options[:page_file_dir] = path
   end
diff --git a/lib/gollum/frontend/app.rb b/lib/gollum/frontend/app.rb
index eadc19e4..ba68923a 100644
--- a/lib/gollum/frontend/app.rb
+++ b/lib/gollum/frontend/app.rb
@@ -238,6 +238,7 @@ module Precious
       @content = @page.formatted_data
       @toc_content = wiki.universal_toc ? @page.toc_data : nil
       @mathjax = wiki.mathjax
+      @css = wiki.css
       @editable = false
       mustache :page
     end
@@ -360,6 +361,7 @@ module Precious
         @content = page.formatted_data
         @toc_content = wiki.universal_toc ? @page.toc_data : nil
         @mathjax = wiki.mathjax
+        @css = wiki.css
         mustache :page
       elsif file = wiki.file(fullpath)
         content_type file.mime_type
diff --git a/lib/gollum/frontend/templates/layout.mustache b/lib/gollum/frontend/templates/layout.mustache
index 05efa0a4..7007dc49 100644
--- a/lib/gollum/frontend/templates/layout.mustache
+++ b/lib/gollum/frontend/templates/layout.mustache
@@ -6,6 +6,7 @@
   <link rel="stylesheet" type="text/css" href="{{base_url}}/css/editor.css" media="all">
   <link rel="stylesheet" type="text/css" href="{{base_url}}/css/dialog.css" media="all">
   <link rel="stylesheet" type="text/css" href="{{base_url}}/css/template.css" media="all">
+  {{#css}}<link rel="stylesheet" type="text/css" href="/custom.css" media="all">{{/css}}
 
   <!--[if IE 7]>
   <link rel="stylesheet" type="text/css" href="{{base_url}}/css/ie7.css" media="all">
diff --git a/lib/gollum/frontend/views/page.rb b/lib/gollum/frontend/views/page.rb
index d232c646..b4e562c3 100644
--- a/lib/gollum/frontend/views/page.rb
+++ b/lib/gollum/frontend/views/page.rb
@@ -80,6 +80,10 @@ module Precious
         @mathjax
       end
 
+      def css # custom css
+        @css
+      end
+
       # Access to embedded metadata.
       #
       # Examples
diff --git a/lib/gollum/wiki.rb b/lib/gollum/wiki.rb
index 1701bcc5..553e3c6b 100644
--- a/lib/gollum/wiki.rb
+++ b/lib/gollum/wiki.rb
@@ -137,6 +137,10 @@ module Gollum
     # Gets the boolean live preview value.
     attr_reader :live_preview
 
+    # Injects custom css from custom.css in root repo.
+    # Defaults to false
+    attr_reader :css
+
     # Public: Initialize a new Gollum Repo.
     #
     # path    - The String path to the Git repository that holds the Gollum
@@ -191,6 +195,7 @@ module Gollum
       @mathjax              = options.fetch :mathjax, false
       @show_all             = options.fetch :show_all, false
       @collapse_tree        = options.fetch :collapse_tree, false
+      @css                  = options.fetch :css, false
     end
 
     # Public: check whether the wiki's git repo exists on the filesystem.