diff --git a/index.html b/index.html
index b129cf0..b056478 100644
--- a/index.html
+++ b/index.html
@@ -7,6 +7,11 @@
     <title>CSS Positioning</title>
     <link rel="stylesheet" href="index.css" />
   </head>
+  <style>
+  {
+  box-sizing: border-box;
+  }
+
   <body>
     <header>
       <a href="./index.html">Home</a>
