The post editor in WordPress doesn't allow you to add custom CSS styles by default. These are some ways to add custom style options to the WordPress post editor. Check them out.

WordPress Custom CSS and JS Editor A simple, lightweight WordPress plugin, allows you to add CSS and JS to your WordPress site with minification. This plugin allows you to add custom site-wide CSS ...

Description Add Custom CSS to your WordPress site without any hassles. An easy-to-use WordPress Plugin to add custom CSS styles that override Plugin and Theme default styles. This plugin is designed ...

Note: To prevent your custom CSS from conflicting with the SFU Common Look & Feel stylesheet, add "custom-" to the front of each class name. For example, if you wish to create a new class called ...

How to Customize CSS in Blogspot. The Blogger Template Designer allows you to insert custom CSS code to change your blog's appearance. You can access the advanced settings of the Template Designer ...