JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" value="run" data-bind="click: troca"></input>

<p class="green" data-bind="css: { blue: interests() }">Hello exists:
</p>

CSS

.green {
    background-color: green;
    border:2px solid red;
}

.blue {
    background-color: blue;
    border:2px solid red;
}

JavaScript

function VM() {
    
    this.interests = false;
    
    this.troca = function(){
    
    	VM.interests(true);
    }
};

ko.applyBindings((new VM()));