how can i add this

Hello adam21s,

Please notice that our theme does not have any such an option that allows you to achieve this effect with the basic theme options, sorry! You should use a plugin with has this functionality or you should have done some changes through the code and use some custom CSS code in order to achieve this effect/style. If you are not aware of the steps which are needed to take in this regard, please consider hiring a freelancer/developer to help you because we cannot provide custom services at the moment, sorry!

Thanks for your understanding!