diff --git a/tildes/scss/modules/_sidebar.scss b/tildes/scss/modules/_sidebar.scss
index d7a56f9..01f1933 100644
--- a/tildes/scss/modules/_sidebar.scss
+++ b/tildes/scss/modules/_sidebar.scss
@@ -4,6 +4,10 @@
     line-height: 1rem;
   }
 
+  details .btn {
+    box-sizing: border-box;
+  }
+
   .btn {
     width: 100%;
   }