Tryit Editor v2.9

Edit This Code:
<!DOCTYPE html>
<html>
<body>

<div id="myDiv" style="border:thick solid green">This is a div.</div>
<br>
<button type="button" onclick="myFunction()">Return border color</button>

<script>
function myFunction() {
    alert(document.getElementById("myDiv").style.borderColor);
}
</script>

</body>
</html>