<!DOCTYPE html>
<style>
.container {
font: 10px/1 Ahem;
color: green;
}
.left {
float: left;
height: 10px;
width: 50px;
background-color: red;
shape-outside: inset(0 100% 0 0);
}
</style>
<body>
You should see a green rectangle. You shouldn't see any red.
<div class="container">
<div class="left"></div>
XXXXX
</div>
</body>