<!DOCTYPE html>
<style>
    .container {
        width: 300px;
        font: 10px/1 Ahem;
    }
    .float {
        float: left;
        width: 100px;
        height: 100px;
        padding: 20px;
        border: 20px solid rgba(0, 0, 0, 0);
        border-radius: 40px;
        margin: 0px;
        background-color: blue;
        -webkit-shape-outside: inset(0px round 40px);
    }
</style>
<body>
    <div class="container">
        <div class="float"></div>
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    </div>
</body>