JSFiddle - React, Tailwind, and code Playground

CSS

.popup {
  display: none;
  position: absolute;
  left:20%;
  top: 20%;
  height: 60%;
  width: 60%;
  background-color: orange;
}

JavaScript

var myownalertbox = {
  
  show: function(message) {
    var popup = document.createElement("DIV");
    popup.className = "popup";
    document.body.appendChild(popup);
    popup.style.display = "block";
    popup.innerHTML = "<div>" + message + "</div>";
    var ybutton = document.createElement("BUTTON");
    ybutton.innerHTML = "YES";
    var nbutton = document.createElement("BUTTON");
    nbutton.innerHTML = "NO";
    ybutton.onclick = function () {
     // do with "YES"
     popup.style.display = "none";
    }
    nbutton.onclick = function () {
     // do with "NO"
     popup.style.display = "none";
    }
    popup.appendChild(ybutton);
    popup.appendChild(nbutton);
  }
}

myownalertbox.show("ARE YOU SURE?");