<!DOCTYPE html>
<html>
<head>
<meta charset="utf8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
body {
    font-family: system-ui;
    -webkit-user-modify: read-write;
    margin: 0;
}

div {
    width: 300px;
    height: 100px;
}

div.drag {
    -webkit-user-select: all;
    border: 1px solid green;
    font-size: 50px;
    line-height: 100px;
    text-align: center;
}

div.drop {
    border: 1px solid tomato;
}
</style>
<script>
addEventListener("load", () => {
    document.querySelector(".drop").addEventListener("drop", event => {
        document.body.style.webkitUserModify = "read-write-plaintext-only";
        document.querySelector("br").remove();
    });
    getSelection().selectAllChildren(document.querySelector(".drag"));
});
</script>
</head>
<body>
    <div class="drag" draggable="true">Drag me</div>
    <div class="drop"><br></div>
    <p>To run the test manually, drag and drop the selected text into the red box.</p>
</body>
</html>