Recently a client of mine wanted to have the post editor in WordPress mimic the styles used on the front-end. And although I’m a big fan of WYSIWYM and rather not use WYSIWYG editors at the end of the day the client pays the bill.
Luckily this specific feature is already build into WordPress. Just add the following line to your theme’s functions.php.
Now you can add styles to your custom-style.css to be used in the post editor. As you can see this is really easy and it’s just one of those things that can make your client’s life a lot easier.