If you want to store html tags in database, there should not be any problem. Then when you need to show them in front end/application, you can just assign them to a label or literal.
But, if you are talking about using font styling in the query window you can always go to
In SQL Server,
Tools --> Options --> Environment --> Fonts & Colors
But, as far I know, you can't apply html tags for styling query window text.
In case you something else, please let me know with little more information.