Face Attendance JS Code

<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
            display: flex;
            justify-content: center;
            align-items: center;
        #main_table {
          font-family: Arial, Helvetica, sans-serif;
          border-collapse: collapse;
          width: 100%;
        #main_table td, #main_table th {
          border: 1px solid #ddd;
          padding: 8px;
        #main_table tr:nth-child(even){background-color: #f2f2f2;}
        #main_table tr:hover {background-color: #ddd;}
        #main_table th {
          padding-top: 12px;
          padding-bottom: 12px;
          text-align: left;
          background-color: #4CAF50;
          color: white;
    <h2>Live Face Attendance</h2>
    <table id ="main_table" style="width:100%">
<!-- The core Firebase JS SDK is always required and must be listed first -->
<script src="https://www.gstatic.com/firebasejs/8.2.2/firebase-app.js"></script>
<!-- TODO: Add SDKs for Firebase products that you want to use
     https://firebase.google.com/docs/web/setup#available-libraries -->
<script src="https://www.gstatic.com/firebasejs/8.2.2/firebase-analytics.js"></script>
<script src="https://www.gstatic.com/firebasejs/8.2.2/firebase-auth.js"></script>
<script src="https://www.gstatic.com/firebasejs/8.2.2/firebase-database.js"></script>
  // Your web app's Firebase configuration
  // For Firebase JS SDK v7.20.0 and later, measurementId is optional
  var firebaseConfig = {
    //paste your configrations here
  // Initialize Firebase
    var d  = new Date();
    var datestring = d.getFullYear()+"-"+
                    ("0"+(d.getMonth()+1)).slice(-2)+ "-"+
                    ("0" + d.getDate()).slice(-2) ;
  var refR = firebase.database().ref().child(datestring);
    var name = snap.child("Name").val();
    var time = snap.child("Time").val();
    var table = document.getElementById("main_table");
    var row = table.insertRow(-1);
    var cell1 = row.insertCell(-1);
    var cell2 = row.insertCell(-1);
    cell1.innerHTML = name;
    cell2.innerHTML = time;