<!DOCTYPE html>
<html>
<head>
<style>
    .container {
        font-family: ahem;
        font-size: 100px;
        overflow: hidden;
        height: calc(1em - 20px);
    }
    span {
        color: transparent;
        background-color: green;
    }
</style>
</head>
<body>
    <div class="container">
        <span>AAAA</span>
    </div>
</body>
</html>
