diff --git a/public/css/icinga/base.less b/public/css/icinga/base.less
index d7fb573d6b..9ce5d7ed48 100644
--- a/public/css/icinga/base.less
+++ b/public/css/icinga/base.less
@@ -194,6 +194,10 @@
 html {
   box-sizing: border-box;
 }
+details > * {
+  // children somehow default to content-box no matter the inheritance
+  box-sizing: border-box;
+}
 *,
 *:before,
 *:after {