<html>
<head>
    <style>
    body {
        margin: 0;
    }

    #textbox {
        position: absolute;
        top: 0;
        left: 0;
        border: 0.5px black solid;
        width: 99px;
        height: 99px;
        background-color: yellow;
    }

    #shadow {
        position: absolute;
        top: 99.5;
        left: 0;
        width: 99px;
        height: 0.5px;
        background-color: #E0E0E0;
    }
    </style>
</head>

<body>
    <div id="textbox" />
    <div id="shadow" />
</body>

</html>