在HTML5中，对于input type="date"字段不显示占位符。如何解决这个问题？

<input placeholder = "Date" class = "textbox-n" type = "text" onfocus = "(this.type = &#39;date&#39;)"  id = "date">

input[type="date"]::before{
   color: #ffffff;
   content: attr(placeholder) ": ";
}
input[type="date"]:focus::before {
   content: "" !important;
}