JSFiddle - React, Tailwind, and code Playground

HTML

<span class="strongSuggestion cls2" data-bind="text: title, css: pepito().length ? myClass1 : myClass" ></span>

CSS

.test{
  color: red
}

.test1{
  color: blue
}

.strongSuggestion {
  font-style: italic;
}

JavaScript

var viewModel={
  myClass: ko.observable('test'),
  myClass1: ko.observable('test1'),
  title: ko.observable('Title'),
  pepito: ko.observable('pepito')
};

ko.applyBindings(viewModel);