JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout-validation/1.0.2/knockout.validation.js"></script>
<span data-bind="validationMessage: test"></span>

<input type="text" data-bind="value: test" />

CSS

.err {
    border: solid 1px red
}

JavaScript

ko.validation.init({
    decorateElement: true,
    errorElementClass: 'err',
    insertMessages: false
});

var vm = {
    test: ko.observable('Delete me').extend({
        required: {
            params: true,
            message: "This is required"
        }
    })
}
ko.applyBindings(vm);