Launch countdown timer with flip animation

I've wanting to do this project(especially the flip animation) ever since I started learning JavaScript which was a few weeks ago. I even tried it in my own experimental files after a few days but couldn't execute the timing function of the flip animations no matter how hard I tried. But now that I have some knowledge, I took this challenge and I'm happy with how it turned out. The logic was a bit tricker than I thought so the code looks a bit messy. There're definitely better ways of doing this but this is my take on the challenge. I also tried the CUBE methodology for CSS but ended up deleting everything and starting over(It's an inappropriate project just to begin with). For the timer, instead of using the actual Date class, I assigned total seconds to localStorage and reset its value once the countdown is done so that it wouldn't stop running even after the time's up(Just for demonstration purpose only). I'd very much love to hear you feedbacks and suggestions on how I can improve further. Happy Coding!