How do I get the value of a CSS attribute with JS?

Question

I am trying this:
var elemento = document.getElementById("circulo1");
var posicion_elemento = elemento.style.left;
alert(posicion_elemento);
but it doesn't work. It is showing me nothing, just blank.

Answer 1

<div class='lll' style="color:red"></div>
var t = document.getElementsByClassName('lll');
console.log(getComputedStyle(t[0]).color);