<form action="welcome.php" method="post" role="form" id="login-form" autocomplete="off">
                    <div class="form-group">
                        <label for="acc" class="sr-only">Cuenta</label>
                        <input type="text" name="acc" id="acc" class="form-control" placeholder="Usuario">
                    </div>
                    <div class="form-group">
                        <label for="pass" class="sr-only">Password</label>
                        <input type="password" name="pass" id="pass" class="form-control" placeholder="Contraseña">
                    </div>
                    <div class="checkbox">
                        <span class="character-checkbox" onclick="showPassword()"></span>
                        <span class="label">Mostrar contraseña</span>
                    </div>
                    <input type="submit" id="btn-login" class="btn btn-custom btn-lg btn-block" value="Ingresar">
                </form>

<?php
require('db.php');
class Usuario {
    function checkUser($acc, $pass){
        require('db.php');
        $data = array($acc, md5($pass));
        $stmt = $connection->prepare("SELECT count(*) FROM usuarios where desc_usuario = ? and password = ? ");

        $result = $stmt->execute($data);

        return $result;
    }
}
?>

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
include('actions/db.php');
include('actions/users/class_users.php');
$acc = $_POST['acc'];
$pass = $_POST['pass'];

$usr = new Usuario();
$user = $usr->checkUser($acc, $pass);
echo $user;