Update pages/css/index.md

Co-Authored-By: emplums <emplums@github.com>

pages/css/index.md

@@ -47,7 +47,7 @@ Primer CSS is built upon systems that form the foundation of our styles such as
 
 <PrimitivesOverview />
 
-## Primer CSS packages
+## Primer CSS bundles
 
 Each component or group of styles is packaged up and distributed via npm. Primer CSS includes 23 packages that are grouped into useful meta-packages for easy install. Each package and meta-package is independently versioned and distributed via npm, so it's easy to include all or part of Primer CSS within your own project.