div#outer {
border: 2px solid green;
}
div#inner {
float: left;
font-family: Verdana;
font-size: 10em;
border: 12px solid rgba(255, 0, 0, 0.5);
width: 80%;
overflow: hidden;
text-align: center;
padding: 20px;
margin: 10px;
background-color: cyan;
background-clip: padding-box;
clip-path: circle(50%);
shape-outside: circle(50%);
-webkit-shape-outside: circle(50%);
}
<div id = "outer">
<span>Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world!</span>
<div id = "inner">Foo bar</div>
<span>Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world! Hello, world! Hello world!</span>
</div>