How to move a particular div to far right? [closed]

I want to display this dark magenta colored box to the far right and also I want that dark magenta colored box to shrink and grow in small/big devices.
Output

body {
    background-color: rgb(79, 211, 79);
}

.cols{
    display: flex;
    flex-basis: auto;
    flex: 1;
    flex-grow: 2em;
    gap: 2em;
    flex-shrink: 1;
    justify-content: flex-start;
}

.far-right{
    margin-left: auto;
    flex-grow: 1em;
    flex-shrink: 1em;
}
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="index.css">
    <script src="index.js"></script>
</head>
<body>
    <div class="bg">
        <div class="cols">
            <div style="background-color: crimson; width: 150px; height: 150px;"></div>
            <div style="background-color: rgb(31, 27, 221); width: 150px; height: 150px;"></div>
            <div id="far-right">
                <div style="background-color: rgb(146, 3, 148); width: 150px; height: 150px;"></div>
            </div>
            
        </div>
    </div>
</body>
</html>