Responsive HTML5 - which is what we have always used.
I just tested Employee Care 3 as shipped with 2019 Classic and searched on "whirl". I got a list of results and clicked the first one, which was the topic already showing. As soon as I clicked, the highlighting appeared.
I tested with the Azure Blue skin using Firefox.
There could be a separate reason for your own project not working but test again using Employee Care 3 in 2019 Classic first.
See www.grainge.org for free RoboHelp and Authoring information.
Thank you, Peter. I will give that sample project a try, too. I will also check it with the Azure Blue skin. Thank you for your reply!