为什么我在_Layout.cshtml的视图顶部留出空间？

我在我的项目中使用asp.net MVC 5。为什么我在_Layout.cshtml的视图顶部留出空间？

在这里，在_Layout.cshtml页面生成的代码：

<body> 
    <div class="navbar navbar-inverse navbar-fixed-top"> 
     <div class="container topNavBtn"> 
      <div class="navbar-header "> 
       <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse"> 
        <span class="icon-bar"></span> 
        <span class="icon-bar"></span> 
        <span class="icon-bar"></span> 
       </button> 
       @Html.ActionLink("Application name", "Index", "Home", new { area = "" }, new { @class = "navbar-brand" }) 
      </div> 
      <div class="navbar-collapse collapse"> 
       <ul class="nav navbar-nav"> 
        <li>@Html.ActionLink("Home", "Index", "Home", new { area = "" }, null)</li> 
        <li>@Html.ActionLink("API", "Index", "Help", new { area = "" }, null)</li> 
       </ul> 
      </div> 
     </div> 
    </div> 
    <div class="container body-content"> 
     @RenderBody() 
     <hr /> 
     <footer> 
      <p>&copy; @DateTime.Now.Year - My ASP.NET Application</p> 
     </footer> 
    </div> 

    @Scripts.Render("~/bundles/jquery") 
    @Scripts.Render("~/bundles/bootstrap") 
    @RenderSection("scripts", required: false) 
</body> 
</html>

我从这个div删除代码：

<div class="navbar navbar-inverse navbar-fixed-top">

创建自己的头：

<body> 
    <header style="background-color:green">My Header</header> 
    <div class="container body-content"> 
     @RenderBody() 
     <hr /> 
     <footer> 
      <p>&copy; @DateTime.Now.Year - My ASP.NET Application</p> 
     </footer> 
    </div> 

    @Scripts.Render("~/bundles/jquery") 
    @Scripts.Render("~/bundles/bootstrap") 
    @RenderSection("scripts", required: false) 
</body>

但在查看我在页面顶部获得空间：