The new WordPress’s HTML editor uses monospace font for editing, which I personally don’t like at all. If you are among folks who don’t appreciate it and want to change, this simple to follow tutorial will help you out.

Procedure:

Note: Do take backup of the files before you try this.

01. Login to your WordPress administration panel and go to Appearance => Editor => Theme Functions (functions.php)

02. Once there place this below code before ?>:

add_action( 'admin_head-post.php', 'devpress_fix_html_editor_font' );
add_action( 'admin_head-post-new.php', 'devpress_fix_html_editor_font' );

function devpress_fix_html_editor_font() { ?>
<style type="text/css">
#editorcontainer #content, #wp_mce_fullscreen {
font-family: Georgia, "Times New Roman", "Bitstream Charter", Times, serif;
}
</style>
<?php }


03. You can change the font to whatever you like.

This concludes this simple and useful tutorial. Hope you like it.