JSFiddle - React, Tailwind, and code Playground

HTML

<button id="btn-a" class="btn" data-bind="css: {'btn-primary':mode() == 'manual'}, click: $root.mode('manual')">Manual</button>
<button id="btn-b"  class="btn" data-bind="css: {'btn-primary':mode() == 'automatic'}, click: $root.mode('automatic')">Automatic</button>
	
<label>MODE: </label><span data-bind="text:mode()"></span>

JavaScript

var TestModel = function() {		
		var self = this;
		this.mode = ko.observable('manual');
	};
	
	var testModel = new TestModel();
	window.testModel = testModel;
	ko.applyBindings(testModel);