PHP - cambiar el color de texto ( input) dependiendo el valor ingresado

<form action ="" method = "POST" name  = "form">

<input type ="text" name = "pagado" placeholder = "ingrese pago" id = "txt">

<?php

include 'documento_total.php';

$pagado =  'pagado';

if ($pagado < $total) {

?>  <style>   #pago {  color: red;  }  </style> <?php

}

else {

?>  <style>   #pago {  color: black;  }  </style> <?php

}

?>

</form>

<input type ="text" name = "pagado" placeholder = "ingrese pago" id = "pago ">

<form action="" method="POST" name="form">

<?php $total = 5; ?>

<input type="text" name="pagado" placeholder="ingrese pago" id="pago">

<input type="hidden" id="total" value="<?php echo $total; ?>">

</form>

<script>

	var pago = document.getElementById('pago');

	var total = document.getElementById('total');

	function check() {

		if (/^[0-9]+$/.test(pago.value) && Number(pago.value) > Number(total.value)) {

			pago.style.color = '#000';

		} else {

			pago.style.color = '#FF0000';

		}

	}

	pago.addEventListener('blur', check);

	check();

</script>