Click event not recognizing textbox in asp.net - asp.net

Question

My click event is showing the error "the name login_password and login_username does not exist in the current context" when I am trying to access my text box from their ids. please help me identify the error as I am just a beginner.
click event:
protected void LogIn_Clicked(object sender, EventArgs e)
{
string usern = "abc";
string pass = "123";
if (login_username.Text == usern && login_password.Text == pass)
{
Response.Redirect("Default.aspx");
}
else
{
label1.Text = "LogIn";
}
}
}
login form:
<form id="login" runat="server">
<h1 style = "Background-color: deepskyblue;">
Log in to your account!</h1>
<p class="register">
<a style = "color: deepskyblue;" href="Login.aspx?logoff=true">Logoff</a>
</p>
<div>
<label for="login_username">
Username</label>
<input type="text" name="username" id="login_username" class="field required" title="Please provide your username" onclick="return login_username_onclick()" />
</div>
<div>
<label for="login_password">
Password</label>
<input type="password" name="password" id="login_password" class="field required"
title="Password is required" />
</div>
<div class="submit">
<asp:Button ID="Button1" Text="Log in" runat="server" OnClick="LogIn_Clicked"
BackColor="#00B2EE" ForeColor="White" />

Answer 1

Those aren't Asp.net Controls. Add the runat="server" attribute:
<input type="text" name="username" id="login_username" class="field required" title="Please provide your username" onclick="return login_username_onclick()" runat="server"/>
Or you can add Asp.net controls:
<asp:TextBox runat="server" ID="login_username" CssClass="field required" ToolTip="Please provide your username"></asp:TextBox>

Answer 2

your inputs for username and password are html only - they need a runat="server" tag to get them in the code behind. The usual way is to use an asp:Textbox though.