JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <tr>
        <td style="width:10px;"></td>
        <td>blah blah blah</td>
    </tr>
</table>

CSS

table
{
    border:1px solid red;
}
tr, td
{
    
min-height:50px;
    border:1px solid #0000ff;
}

JavaScript

var divBgTop=0;
function initDivTop(){
    var mdiv = document.getElementById("divBg");
    divBgTop=mdiv.offsetTop;
    alert(divBgTop);
    alert(mdiv.clientTop);
    mdiv.style.top=300 + "px";
    alert(mdiv.clientTop);
    divBgTop=mdiv.offsetTop;
    alert(divBgTop);
}