Code Blocks is a WordPress plugin that adds a tool to post codes in post. Code Blocks can be configured. It also can be used to add Custom CSS to WordPress Visual Editor.
You can download the plugin from WordPress. Simply search for Code Blocks in WordPress Plugins Add New page or you can download the plugin from here.
You can seek help using the comments on this page and the plugin author (me) will certainly help you for sure if I’m not in the conditions mentioned in this page.