JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout-validation/2.0.3/knockout.validation.js"></script>
<script src="https://code.jquery.com/jquery-3.1.1.min.js"></script>
<div>
   Mandatory field:
</div>
<span>
   <span data-bind="validationMessage: userInput"></span>
   <input type="text" data-bind="textInput: userInput" />
</span>

CSS

.field-validation-error {
    color: #dd1e25;
}

TypeScript

class MyViewModel {
    constructor(userInput: string) {        
        this.userInput(userInput);
    }
    
    userInput = ko.observable('').extend({
        required: {
            params: true,
            message: 'Please enter a value.'
        }
    });
}

 $(function () {
 		ko.validation.init({
      insertMessages: false,
      errorMessageClass: 'field-validation-error',
    	insertMessages: true
    });

   window.vm = new MyViewModel('Delete me');

   ko.applyBindings(window.vm);
 });