diff --git a/src/client/theme-default/styles/components/custom-block.css b/src/client/theme-default/styles/components/custom-block.css
index f4527868..7af89807 100644
--- a/src/client/theme-default/styles/components/custom-block.css
+++ b/src/client/theme-default/styles/components/custom-block.css
@@ -118,6 +118,7 @@
   margin: 0 0 8px;
   font-weight: 700;
   cursor: pointer;
+  user-select: none;
 }
 
 .custom-block.details summary + p {