I'm wondering why you'd have prompt in the first place since you have the required attribute. This all reeks of using JavaScript to do things that are NONE of Javascript's business.

But that stands to reason with the static style in the scripting, CSR, illegible colour contrasts, fixed positioning cutting off content at small display sizes, and the rest of the middle-fingers to usability and accessibility so common when people try to use JS for things it's just not meant for.