script.js

let  countDate = new Date('April 13, 2021 00:00:00').getTime();

function thinGyan(){
    let now = new Date().getTime();
        gap = countDate - now;

        let second = 1000;
        let minute = second * 60;
        let hour = minute * 60;
        let day = hour * 24;

        let d = Math.floor(gap / (day));
        let h = Math.floor((gap % (day)) / (hour));
        let m = Math.floor((gap % (hour)) / (minute));
        let s = Math.floor((gap % (minute)) / (second));

        document.getElementById('day').innerText = d;
        document.getElementById('hour').innerText = h;
        document.getElementById('minute').innerText = m;
        document.getElementById('second').innerText = s;

}

    setInterval(function(){
        thinGyan();
    },1000)

    // window.addEventListener("DOMContentLoaded", event => {
    //     const audio = document.querySelector("audio");
    //     audio.volume = 0.2;
    //     audio.play();
    //   });