<!DOCTYPE html>

<html>
<head>
    <style>
        .parent {
            position: absolute;
            top: 50px;
            left: 50px;
            width: 100px;
            height: 100px;
            padding: 20px;
            outline: 1px solid black;
            transform: translateZ(0);
        }
        .box {
            height: 100%;
            width: 100%;
            overflow: hidden;
            background-color: green;
            filter: blur(2px);
        }
        
        .masker {
            position: absolute;
            top: 64px;
            left: 64px;
            width: 112px;
            height: 112px;
            border: 13px solid black;
            box-sizing: border-box;
        }
        
    </style>
</head>
<body>
    <div class="parent">
        <div class="box">
        </div>
    </div>
    
    <div class="masker">
    </div>
</body>
</html>