Adding Custom CSS style in Markup drop down of Sharepoint 2010 HTML editor ribbon

1. Create one css file in 14 hive(you can add it in your visual studio solution by adding layouts mapped folder)

2. add below css class in that file 

/* custom style in */

DIV.ms-rteElement-mkg-H1

{

-ms-name: "marketing-header";

color: #d65c26;

font-family: Verdana,Geneva,sans-serif;

font-weight: normal;

font-size: 2em;

}

3. Deploy solution

4. add css file link on page where you want the custom option(you can also add it in master page)

<link href="/_layouts/css/Custom.css" rel="stylesheet" type="text/css" />

5. refrshh the page

6. Edit the page

7. Check the markup style dropdown

 

:)