How to Add a diffrent FONT in this script? [duplicate]

Hello all i have this script running how do i add a font in this? I Not that good at this but i,m learning . I tryed some thinks so i need some help at this.

<!DOCTYPE html>
<html>
<style>

body {
  background-image: url('****/*****/Weerbericht_Achterhoek.jpg');
  background-repeat: no-repeat;  
  background-attachment: fixed;
  background-size:  100% 100%;
</style>
<body>


<iframe id="myFrame" frameborder="0" scrolling="no" style="height:800px;width:8000px;border:none;" src='https://****/****/loadknmi.php'></iframe>
<script>
var frame = document.getElementById('myFrame');
frame.onload = function () {
var body = frame.contentWindow.document.querySelector('body');
body.style.color = 'white';
body.style.fontSize = '23px';
body.style.lineHeight = '20px';



};
</script>



</body>
</html>