JSFiddle - React, Tailwind, and code Playground

HTML

<div class="screenprint">
<div class="placements">
                <label for="first">First placement</label>
                <select >
                    <option value="0">None</option>
                    <option value="">Left </option>
                    <option value="">Right </option>
                    <option value=""> front</option>
                    <option value=""> back</option>
                </select>
          
            </div>
            <div class="color">
                <h3>No. of colors</h3>
                <label >For 1st placement</label>
                <select disabled name="color">
                    <option value="1">1</option>
                    <option value="2">2</option>
                    <option value="3">3</option>
                    <option value="4">4</option>
                    <option value="5">5</option>
                    <option value="6">6</option>
                </select>
             
            </div>
</div>

JavaScript

var screenprint = document.getElementsByClassName('screenprint')[0];

var sp = screenprint.getElementsByClassName('placements')[0].getElementsByTagName('select');

for (var i = 0; i < sp.length; i++) {
	sp[i].onchange = function(t){

		if(this.value!==0){
			screenprint.getElementsByClassName('color')[0].getElementsByTagName('select')[i].disabled= false;
		}
		else{
			screenprint.getElementsByClassName('color')[0].getElementsByTagName('select')[i].disabled= true;
		}


	}
};