JSFiddle - React, Tailwind, and code Playground

HTML

<div id="xdiv" style="width:100px; height:100px; border: solid 1px black" />

JavaScript

document.getElementById("xdiv").onmousemove = function(e) {
    var evt = e || event;
    
    if (this.offsetWidth - evt.offsetX > 10) {
        this.style.backgroundColor = "red"
    } else {
        this.style.backgroundColor = "green"
    }
    
    
}