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Maybe make two text boxes: one with highlighting and one without.
Then you can show and hide the text boxes based on a variable that you can control with the button.
Here is a link to the Button object help along with all the available actions and what they do and which ones are not supported by Ajax etc. too.
https://help.qlik.com/en-US/qlikview/November2018/Subsystems/Client/Content/QV_QlikView/Button2.htm
Hopefully this helps a little. Not sure if there is a specific action to do what you want now that I think about it, but I will let you review things to confirm for yourself. Just scroll down to the Action section in the link, that is where you want to be for all the details on those.
Regards,
Brett