<a href="<?= URL_SITIO; ?>" class="btn fa fa-arrow-left">Volver</a>
<form action="" method="POST" id="fmPass">
    <h1>Cambiar contraseña:</h1>
    <?php if ($_error_post) { ?>
        <div class="error"><?= $_error_post ?></div>
    <?php } ?>
    <input type="password" placeholder="Contraseña anterior" name="OLD_PASS" id="pass3" value="" />
    <input type="password" placeholder="Contraseña nueva" name="PASS" id="pass2" value="" />
    <input type="password" placeholder="Repetir Contraseña" name="CONFIRM_PASS" id="repass2" value="" />
    <input type="submit" name="action" value="Guardar" />
</form>