No sure if this is what you are referring to but anyway if you don’t already have a child theme or a custom.css you should install a plugin like custom CSS plugin then add the following to the custom css area.
Thanks a lot for your prompt reply , Salasturation.
I have done exactly as you said. However, there is still a small portion of the topbar which is still visible.
I really need the topbar to disappear as it is white and my background is black. Is there any workaround? Thanks in advance.