JSFiddle - React, Tailwind, and code Playground

HTML

<span id="spnTest">500</span>
<button id="btnTest" onclick="javascript:decrease()">Decrease</button>

JavaScript

var ratio = 25;
var totalValue = 500;

function decrease(){
    if(totalValue == 0) return;
    totalValue -= ratio;
    document.getElementById('spnTest').innerHTML = totalValue;
}
document.getElementById('btnTest').onclick = function(){ decrease(); }