<!DOCTYPE html>
<html>
<body>

<p>Click the button to get all the computed styles for the test div.</p>
<p><button onclick="myFunction()">Try it</button></p>
<div id="test" style="height: 50px;background-color: lightblue;">Test Div</div>
<p>The computed styles for the test div are: <br><span id="demo"></span></p>

<script>
function myFunction(){
    var elem = document.getElementById("test");
    var txt = "";
    cssObj = window.getComputedStyle(elem, null)

    for (i = 0; i < cssObj.length; i++) {
        cssObjProp = cssObj.item(i)
        txt += cssObjProp + " = " + cssObj.getPropertyValue(cssObjProp) + "<br>";
    }
    document.getElementById("demo").innerHTML = txt;
}
</script>

</body>
</html>