JSFiddle - React, Tailwind, and code Playground

HTML

<td>
            <select name="sizi_pixel" id="drp">
                <option value="100">100 Pixels</option>
                <option value="200">200 Pixels</option>
                <option value="350">350 Pixels</option>
                <option value="450">450 Pixels</option>
                <option value="600">600 Pixels</option>
            </select>
</td>

<div id="myDiv" style=" border-width:3px;border-style:solid;border-color:#ff9900; height:400px; width:300px">

                    <input class="color" value="999">
                            <input class="color" value="999">
                            <input class="color" value="999">
               </div>

JavaScript

document.getElementById('drp').addEventListener('change', changeSize);

function changeSize() {
    var myDiv = document.getElementById('myDiv');
    var selectbox = document.getElementById('drp');

    var index = selectbox.selectedIndex;
    var value = selectbox[index].value;

    myDiv.style.width = value + 'px';
}