How do I removed my pink alert message box i created in css after a few seconds?

I created an alert message box where if the use chooses none of the three options that are listed , a pink alert message appears below the bottom of the button asking the user to choose one of the three options in the select menu. I had setTimeout function but it doesn’t removed the alert class I created.
here is a link to my code
https://codepen.io/noblegas/pen/wvaxYmY