Update header.html

docs/_includes/header.html

@@ -3,7 +3,8 @@
   background-color: #555;
   color: white;
   float: left;
-  border: none;
+  border: 1px;
+  border-style: solid;
   outline: none;
   cursor: pointer;
   padding: 14px 16px;
@@ -12,6 +13,7 @@
 
 .headerlink:hover {
   background-color: #777;
+  color: white;
 }
 </style>