index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel= "icon" href="https://image.flaticon.com/icons/png/128/2972/2972531.png">
    <link rel= "stylesheet" href="./index.css">
    <title>Clock</title>
</head>
<body onload="time()">
    <div id= "txt"></div>

    
 <script>
    function time() {
    const today = new Date();
    let hour = today.getHours();
    let min = today.getMinutes();
    let sec = today.getSeconds();
     min = checkTime(min);
    sec = checkTime(sec);
    document.getElementById('txt').innerHTML = hour + ":" + min + ":" + sec;
    setTimeout(time, 1000);
}

    function checkTime(x){
    if (x < 10){
        x = "0" + x;
    }
    return x;
}


</script>
</body>
</html>