首先，有两件事:

For a start, 2 things:

1. 具有runat="server"的控件成为服务器端控件(因此可以在后面的代码中访问)
   
2. 在代码隐藏中创建的控件是服务器端控件
   

1. Controls having runat="server" become a server side control (thus accessible in code behind)
   
2. Controls that are created in code-behind are server side controls
   

所有ASP.NET控件都是服务器端，而HTML控件是客户端.您可以通过分配runat=server 属性将HTML控件转换为服务器端.

All ASP.NET controls are server side and HTML controls are Client Side. You can turn HTML controls into server side by assigning runat=server attribute.