[Javascript]How to change td.style when dynamic add table row

[Javascript]How to change td.style when dynamic add table row

I use javascript to add table rows dynamically, but I don't know how to
change the style of the table data. My code is:
var tableis = document.getElementById("cameraTable");
var last=(-1);
var Tr = tableis.insertRow(last);
var Td1 = Tr.insertCell(0);
Td1.innerHTML="<div name='mac"+i+"' id='mac"+i+"'>"+mac+"</div>";
Tr.appendChild(Td1);
and I only know how to change the background of the td:
Td1.bgColor="#00FF00";
I want to change the border style of the td, is it possible? The style is
like:
style="border: 1px solid black;"
I have tried Td1.style="border: 1px solid black;" but it is no effort.
Any answer appreciated.