JSFiddle - React, Tailwind, and code Playground

HTML

<table id="Table" style="width:100%" contenteditable >
    <tr>
    <th id="Name" bgcolor= #00FFCC >Name</th>
    <th id="ID" bgcolor= #00FFCC>ID</th>
    <th bgcolor= #00FFCC >Assignment 1</th>
    <th contenteditable = false bgcolor= #00FFCC >Final</th>
    </tr>
    <tbody>
    <tr id="Row">
    <td contenteditable='true'>Scott Richardson </td>
    <td contenteditable='true'>123456</td>
    <td contenteditable='true' id= "Right" onblur= "Function()">-</td>
    <td id="Final" contenteditable='false'></td>
    </tr>
    </tbody>
    </table>
    
    <button id="average" id="button" class="button1" onclick="average()">Calculate grade</button>
    <button onclick= "Function()" id="button" class="button1">Add row</button>
    <button type="button" class="button1"onclick="AddColumn()">Add Column</button>
    <button type = "button" class="button1">
    Save Cookie</button>
    <button type = "button" class="button1">Load Cookie
    </button>

CSS

table,
th,
td 
{
  border: 1px solid black;
  font-family: sans-serif;
}

JavaScript

var assignment =1;
average = function() 
{
   var table = document.getElementById("Table");
   var rows = table.rows;
   var nsub=0;
   var int = 0;
   
   
   for (var i = 1; i < rows.length; i++) 
   {
     var cells = rows[i].cells;
     var sum = 0;
		 var num = 0;
     
      for (var x = 2; x < (cells.length -1); x++) 
      { 
       var cell = cells[x];
       var add = parseInt(cell.innerHTML);
       
       if(!isNaN(add)) 
       {       
          sum += add;
          num++;
       }
         else
         {
           nsub ++;
         }
       
     }
   
   }
   
   var avg = sum / num;
   rows[i].cells[cells.length -1].innerHTML = "<td>" + Math.round(average) + "%" + "</td>";
   
   if(avg < 40)
   {
           rows[i].cells[cells.length -1].style.backgroundColor= "red";
           
   }
      else
      {
           rows[i].cells[3].style.backgroundColor= "white";
           rows[i].cells[3].style.color="black";

        
      }
   

}