How to use html button in asp.net backend coding

if you are using Asp.net Webforms :- 

protected void SubmitButton_Click(object sender, EventArgs e)
{
    // Handle the button click on the server-side
    // Your server-side code goes here
}
if you are using Asp.net MVC View :- 

@using (Html.BeginForm("Submit", "YourControllerName", FormMethod.Post))
{
   
   
}
Controller (YourControllerNameController.cs):

public class YourControllerNameController : Controller
{
    // Other actions if any

    [HttpPost]
    public ActionResult Submit()
    {
        // Handle the form submission on the server-side
        // Your server-side code goes here

        return View(); // You can redirect to another view or return a response as needed
    }
}

Please select which one is acceptable with your requirement.
 

If you want to handle the click event of the HTML button in ASP.NET without using JavaScript, you can use the runat="server" attribute in the tag and handle the button click event on the server side using C#

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="YourPage.aspx.cs" Inherits="YourNamespace.YourPage" %>