When you drag and drop controls from the HTML Tab of the toolbox in visual studio, they get rendered as static HTML controls. If you want these controls to be accessed by the server then you will have to convert them to HTML server controls.
To convert a HTML control into an HTML server control, right click the HTML control and select, “Run as server control”.
Note that server controls also have a property called runat=”server”. The HTML controls will not have this property, but the converted controls will.
You can also distinguish a server control by the presence of a glyph( a small arrow head) on it, in the design view tab.