How to get the element Background Color in JavaScript

Use style.background on the specific div element.

document.getElementById("yourElementId").style.background;

Example:

<div id="box" style="background: green; width: 40px; height: 50px;"></div>

<script>
    var backgroundColor = document.getElementById("box").style.background; 
    console.log(backgroundColor)
</script>

Output (console): green