diff --git a/mkdocs.yml b/mkdocs.yml
index ade6dc6..c1b7395 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -151,7 +151,8 @@ extra_css:
   # Shared AgenTrust editorial design system. Deliberately the only stylesheet:
   # a local override here is how this site drifted to the Material default
   # violet last time. Change the shared file instead.
-  - https://agentrust-io.com/design-system.css
+  # The ?v= matches CSS_VERSION in agentrust-io.github.io tools/site_header.py. Browsers keep these files for hours, so bump it there and here together.
+  - https://agentrust-io.com/design-system.css?v=21
 
 nav:
   - Home: index.md
@@ -181,4 +182,5 @@ nav:
       - Privacy: PRIVACY.md
 
 extra_javascript:
-  - https://agentrust-io.com/supernav.js
+  # The ?v= matches CSS_VERSION in agentrust-io.github.io tools/site_header.py. Browsers keep these files for hours, so bump it there and here together.
+  - https://agentrust-io.com/supernav.js?v=21