<p>
    There should not be any non-white pixels inside this box:    
</p>
<div style="border: solid; height: 100px; width: 100px; padding: 50px;">
    <div style="width: 100px;
        height: 100px;
        -webkit-box-shadow: 20px 20px white;
        -webkit-transform: rotate(45deg);
    "></div>
</div>