<select class="un">
        <option class="op" value="" disabled selected style="color:gray">Username</option>
        <?php foreach ($result as $output) { ?>
    <option class="op"> <?php echo $output["firstname"]." ". $output["lastname"]; ?></option>
<?php } ?>
            </select>
      <input class="pass" type="password"  placeholder="Password">
      <a class="submit" align="center">Sign in</a> <select class="un">
            <option class="op" value="" disabled selected style="color:gray">Username</option>
            <?php foreach ($result as $output) { ?>
        <option class="op"> <?php echo $output["firstname"]." ". $output["lastname"]; ?></option>
    <?php } ?>
                </select>
          <input class="pass" type="password"  placeholder="Password">
          <a class="submit" align="center">Sign in</a>

<!-- begin snippet: js hide: false console: true babel: false -->

$message="";
if(count($_POST)>0) {
    //$conn = mysqli_connect("localhost","root","","phppot_examples");
    $result = sql($db, "SELECT * FROM user_details WHERE firstname='" . $_POST["firstname"] . "' and password = '". $_POST["pdw"]."'");
    //$result = mysqli_query($conn,"SELECT * FROM users WHERE user_name='" . $_POST["userName"] . "' and password = '". $_POST["password"]."'");
    $count  = rowCount($result);
    if($count==0) {
        $message = "Invalid Username or Password!";
    } else {
        $message = "You are successfully authenticated!";
    }
}