This is a quick tip about how to get rid of the scrollbar from the WordPress category post editor page. Just add the following code to your theme’s functions.php.

add_action('admin_head', 'remove_category_scrollbars');
function remove_category_scrollbars() {
echo '
<style type="text/css">
#category-all.tabs-panel {height: auto;}
</style>
';
}

The above code adds some CSS into the WordPress header. The admin_head action event makes sure that the CSS only gets added to the admin area. Take a look at the HTML markup of the WP admin area. With the help of admin_head and CSS you can change the appearance of almost anything you want.