diff --git a/book.toml b/book.toml
index 521f93cbb1d..dfb66f10955 100644
--- a/book.toml
+++ b/book.toml
@@ -18,7 +18,7 @@ create-missing = false
 # Remove the numbers that appear before each item in the sidebar, as they can
 # get quite messy as we nest deeper
 no-section-label = true
-additional-css = ["docs/css/custom.css"]
+additional-css = ["docs/lib/custom.css"]
 
 # The source code URL of the repository
 git-repository-url = "https://github.com/vector-im/element-web"
diff --git a/docs/css/custom.css b/docs/lib/custom.css
similarity index 100%
rename from docs/css/custom.css
rename to docs/lib/custom.css