diff --git a/environment.yml b/environment.yml
index a696029b..517dd39c 100644
--- a/environment.yml
+++ b/environment.yml
@@ -7,7 +7,7 @@ dependencies:
   - pip
   - pip:
     - jupyter-book==1.0.4post1
-    - quantecon-book-theme==0.20.3
+    - quantecon-book-theme==0.21.0
     - sphinx-tojupyter==0.6.0
     - sphinxext-rediraffe==0.3.0
     - sphinx-exercise==1.2.1