JavaScript نافذة او شباك getComputedStyle() Method

<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>

<div id="test" style="height: 50px;background-color: lightblue;">Test Div</div>
<p>The computed font size for div::first-letter in the test div is: <span id="demo"></span></p>

<script>
function myFunction(){
    var elem = document.getElementById("test");
    var theCSSprop = window.getComputedStyle(elem, "first-letter").getPropertyValue("font-size");
    document.getElementById("demo").innerHTML = theCSSprop;
}
</script>