fix(styles): implement flex layout for body element

www/index.html

@@ -9,6 +9,13 @@
 
     <style>
 
+        body {
+            margin: 0;
+            padding: 0;
+            display: flex;
+            flex-direction: column;
+        }
+
         table tbody td {
             font-size: 13px;
         }