LayoutTests/fast/box-shadow/negative-inset-box-shadow.html

<style>
    div {
        position: absolute;
        top: 10px;
        left: 10px;
        box-shadow: rgba(0,0,0,0) 0px 0px 50px -25px inset;
        height: 50px;
        width: 50px;
    }
</style>
<div></div>