diff --git a/_config.yml b/_config.yml
index 5728758b4..980ad45a2 100644
--- a/_config.yml
+++ b/_config.yml
@@ -40,6 +40,7 @@ defaults:
         - jsx
         - bash
         - scss
+        - css
         - elixir
         - ruby
 
diff --git a/css-flexbox.md b/css-flexbox.md
index a6d8f3924..eaa491de7 100644
--- a/css-flexbox.md
+++ b/css-flexbox.md
@@ -3,6 +3,7 @@ title: CSS flexbox
 category: CSS
 layout: 2017/sheet
 updated: 2017-08-29
+prism_languages: [css]
 weight: -3
 ---