UPDATE: You just have to put this code in your custom-css area in the wordpress customizer:
.wpb_wrapper {font-family: playfair display;}
But this will affect all items on your site with the CSS-Class “.wpb_wrapper” so maybe you should look for a way to specifice the CSS-Classes and CSS-IDs for single elements of your page if you have to, so that you’re able to specify your CSS-Code, when you need some like now, to point just at the one specified Element.