diff --git a/static/css/main.css b/static/css/main.css
index 8f1fd406..e554c124 100644
--- a/static/css/main.css
+++ b/static/css/main.css
@@ -128,6 +128,12 @@ aside#toc {
     margin-left: -15rem;
     font-size: 90%;
     line-height: 1.2;
+    opacity: .2;
+    transition: opacity .5s;
+  }
+
+  aside#toc:hover {
+    opacity: 1;
   }
 
   aside#toc h2 {