Update default.html

Signed-off-by: David Rotermund <54365609+davrot@users.noreply.github.com>

_layouts/default.html

@@ -150,6 +150,10 @@
           display: none; /* This will make an empty header cell vanish */
         }    
 
+        table, th, td {
+          border: 2px solid white; /* 2px lines for cells and header */
+        }
+        
         img {
           display: block;
           margin-left: auto;