diff --git a/default_environment/stylesheet/main.css b/default_environment/stylesheet/main.css
index 6bcedde..95473df 100644
--- a/default_environment/stylesheet/main.css
+++ b/default_environment/stylesheet/main.css
@@ -44,6 +44,10 @@
   }
 }
 
+* {
+  box-sizing: border-box;
+}
+
 body {
   color: var(--site-text-color);
   background-color: var(--site-background-color);