JSFiddle - React, Tailwind, and code Playground

CSS

body { background-color:lime }

JavaScript

function getBackground(){
 	
    var getBody = document.getElementsByTagName("body")[0]
    var prop = window.getComputedStyle(getBody).getPropertyValue("background-color");

	if(prop === "transparent"){
		//console.log("No background colour set")
        alert("No background colour set")
	} else {
		//console.log(prop);
        alert(prop)
	}
   }

  getBackground();