diff --git a/.github/workflows/doc.yml b/.github/workflows/doc.yml
index a370ee57..4df4ba14 100644
--- a/.github/workflows/doc.yml
+++ b/.github/workflows/doc.yml
@@ -12,7 +12,7 @@ jobs:
     - name: Create Build Environment
       run: |
         sudo apt install -y doxygen virtualenv npm
-        sudo npm install -g less
+        sudo npm install -g less clean-css
         cmake -E make_directory ${{runner.workspace}}/build
 
     - name: Configure