<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Reference</title>
<style>
.clamp {
display: flow-root;
font: 16px / 32px serif;
white-space: pre;
padding: 0 4px;
background-color: yellow;
}
.ifc {
display: flow-root;
background-color: orange;
}
</style>
<div class="clamp">Line 1
Line 2
Line 3
Line 4
<div class="ifc">Line 5
Line 6</div></div>