Maintain keyboard focus on button across multiple slides

I am working on an HTML5 project in Captivate 2017.  The project must be 508 compliant therefore I have created custom navigation as the built in table of contents and playbar did not meet the requirements.  What I have not been able to work out is if it is possible to keep keyboard focus on a button across multiple slides.  I have placed my custom navigation buttons on the first slide and made visible for the rest of the project.  I can use the keyboard to navigate but when I tab and have a button highlighted, and then slide moves on to the next slide I loose the keyboard focus.  The built in playbar doesn't do this - it keeps keyboard focus until a user performs an action - which is what I need but unfortunately other features in the playbar mean that I cannot use it.  Is there anyway to have custom navigation and maintain keyboard focus throughout the project?