<style>
    .container {
        width: 100px;
        height: 100px;
        overflow: hidden;
        display: inline-block;
    }
    .box {
        width: 800px;
        height: 800px;
        background-color: green;
    }
    .gaussian-blur {
        filter: url(#gaussian-blur);
        transform: translate(-300px, -300px);
    }
</style>
<body>
    <div class="container">
        <div class="box gaussian-blur"></div>
    </div>
    <svg height="0">
        <filter id="gaussian-blur">
            <fegaussianblur stdDeviation="100">
        </filter>
    </svg>
</body>