<!DOCTYPE html>
<html>
<head>
<style>
div {
    border: 1px solid green;
}

div > div {
    border: 1px solid red;
}
</style>
</head>
<body>
<div style="width: 200px;">
    <div style="width: 200px; height: 50px"></div>
</div>

<div style="width: 200px; max-height: 50px;">
    <div style="height: 200px; width: 200px;"></div>
</div>

<div style="width: 200px; min-height: 300px">
    <div style="height: 50px; width: 200px;"></div>
</div>
</body>
</html>