<!doctype html>

 <style>
    html {
        font: 16px Times;
    }

    #content {
        -webkit-flow-into: flow1;
        padding: 5px;
    }
    
    #first-box {
        border: 1px solid blue;
    }
    
    #second-box {
        margin:auto;
        border: 1px solid green;
        width:75%;
        overflow:hidden
    }
    
    #region1, #region2, #region3 {
        border: 1px solid black;
        -webkit-flow-from: flow1;
    }

    #region1 {
        width: 300px;
        height: 100px;
    }
    
    #region2 {
        width: 400px;
        height: 180px;
    }
    
    #region3 {
        width: 220px;
        height: 120px;
    }
    
    .float { width:50px; height:50px; background-color: lime }
    .left { float: left }
    .right { float: right }
</style>

<body>
<p>The first and last lines of text in the regions below should be clipped to the green box. The overflow
section sizes itself and clips differently in each region. The green box should start below the lime floats.</p>

<div id="content">
    <div id="first-box">
        <div class="float left"></div> <div class="float right"></div>
        <div id="second-box">
            <div style="width:500px">Clipped line of text that should not be visible.</div>
            <p>These lines will not spill out of the regions. These lines will not spill out of the regions.
            These lines will not spill out of the regions. These lines will not spill out of the regions. </p>
            <p>These lines will not spill out of the regions. These lines will not spill out of the regions.
            These lines will not spill out of the regions. These lines will not spill out of the regions. </p>
            <div style="width:500px">Clipped line of text that should not be visible.</div>
        </div>
    </div>
</div>

<div id="container">
    <div id="region1"></div>
    <div id="region2"></div>
    <div id="region3"></div>
</div>