how to use html input text in C#

how to use html input text in aspx.cs page without using runat="server"

Default.aspx:




Default.aspx.cs:

string aa="hello";

txtname.value =aa; ---> how to use
//string value pass to textbox how?
//how to call this txtname(textbox) in cs page ?

Reply me quick....................
help me plzzzzzzzzzzzzzzzzzz