js64my.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

<style>

    body {
        color: red;
        margin: 5px;
    }

</style>


</head>
<body>
    
    <p id="p1"></p>


    <!-- Узнать все установленные стили -->

    <script>

        let computedStyle = getComputedStyle(document.body);
        alert(computedStyle.length);

        let s = '';

        for (i=0; i<computedStyle.length; i++) {
            sv =  computedStyle[i];
            s += `<br>${sv}: ${computedStyle[sv]}`;

        }


        p1.innerHTML = s;

    </script>


</body>
</html>