Please how do I fix button click event using bootstrap theme

Question

Good day everyone please i am having challenges to have a button click event in my asp.net project when ever i try to click on my bootstrap theme when designing button it does not take me to the asp.net webform eg(default.aspx.cs) instead it takes me to the default.aspx. so i am unable to write my code under the button without using the asp.net drag and drop button.

<button ID="btnlogin" class="btn btn-primary btn-block btn-flat" type="submit" runat="server" oneserverclick="btnlogin_onClick" >Sign in </button>

this code is not working. i want whereby whenever i click on the button it makes something like this

protected void btnlogin_Click(object sender, EventArgs e)
{
where i can write code like this
protected void btnlogin_Click(object sender, EventArgs e)
{
SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["loginConnectionString1"].ToString());
con.Open();
string query = "select count (*) from log where username ='" + txtuser.Text + "' and password ='" + txtpass.Text + "' ";
SqlCommand cmd = new SqlCommand(query, con);
string output = cmd.ExecuteScalar().ToString();

for registration and other codes