a.diff

diff --git a/Rakefile b/Rakefile
index adc9079..60348dd 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,9 +1,13 @@
 ENV['TZ'] = "America/Los_Angeles"
 require 'erb'
+require 'fileutils'
 
 desc "build static files"
 task :build do |t|
   system "bundle exec jekyll build"
+  time = Time.now.to_i
+  system "find _site -name \\*.html | xargs perl -i -nlpe 's/screen\\.css/screen-#{time}.css/'"
+  FileUtils.cp("_site/css/screen.css", "_site/css/screen-#{time}.css")
 end
 
 desc "push site content to the production environment"