add styling for tables in markdown preview

www/code/inner.html

@@ -86,6 +86,13 @@
             max-width: 40vw;
             margin: auto;
         }
+        #preview table tr td, #preview table tr th {
+            border: 1px solid black;
+            padding: 15px;
+        }
+        #preview table tr th {
+            border: 3px solid black;
+        }
     </style>
 </head>
 <body>