diff --git a/core/modules/system/css/system.theme.css b/core/modules/system/css/system.theme.css
index 3a8bddb..931a36a 100644
--- a/core/modules/system/css/system.theme.css
+++ b/core/modules/system/css/system.theme.css
@@ -4,6 +4,16 @@
  */
 
 /**
+ * Universal Box Sizing with Inheritance
+ */
+.html {
+  box-sizing: border-box;
+}
+*, *:before, *:after {
+  box-sizing: inherit;
+}
+
+/**
  * Publishing status.
  */
 .node--unpublished {