When my website is visited there is two buttons. One that says register and one that says login. When pressed a CSS popup will appear. Im trying to make this popup work for the register. How would i do this? here is the code

Code:
	<a href="#x" class="overlay" id="join_form"></a>
        <div class="popup">
            <h2>Sign Up</h2>
            <p>Please enter the details you would like to<br>
			register with here. You MUST be <br>atleast thirteen
			to register.</p><br>

            <div>
                <label for="email">Email</label>
                <input type="text" id="email" value="" />
            </div>
            <div>
                <label for="pass">Password</label>
                <input type="password" id="pass" value="" />
            </div>
            <div>
                <label for="firstname">First name</label>
                <input type="text" id="firstname" value="" />
            </div>
            <div>
                <label for="lastname">Last name</label>
                <input type="text" id="lastname" value="" />
            </div>
			<div>
			<label for="sex">Sex</label>
			<input type="radio" name="sex" value="male">Male
			<input type="radio" name="sex" value="female">Female
			</div>