Paste the below given code into functions.php

add_action( ‘admin_head-post.php’, ‘phpcodez_editor_font’ );
add_action( ‘admin_head-post-new.php’, ‘phpcodez_editor_font’ );

function phpcodez_editor_font() { ?>
<style type=”text/css”>#editorcontainer #content, #wp_mce_fullscreen { font-family: “Times New Roman”, Verdana, }</style>
<?php }