box-sizing: border-box;

Author: simonw

qr.html

@@ -6,6 +6,9 @@
     <title>QR Code Decoder</title>
     <script src="https://cdn.jsdelivr.net/npm/jsqr@1.4.0/dist/jsQR.min.js"></script>
     <style>
+        * {
+            box-sizing: border-box;
+        }
         body {
             font-family: Arial, sans-serif;
             max-width: 800px;