css/css-flexbox/negative-margins-001.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Flexible Box Test: Negative margins</title>
<link rel="author" title="Google Inc." href="https://www.google.com/">
<link rel="help" href="http://www.w3.org/TR/css-flexbox-1/#item-margins">
<link rel="match" href="reference/negative-margins-001-ref.html">
<meta name="assert" content="Tests that for intrinsic size computations,
an item may take up less than zero space when it has negative margins.">
<style>
    .container {
        width: 40px;
        background-color: red;
        line-height: 0px;
        border: 3px black solid;
    }

    .flex {
        display: inline-flex;
        background-color: green;
    }

    .item {
        width: 20px;
        height: 10px;
        background-color: green;
    }

    .first {
        width: 40px;
    }

    .neg-marg {
        margin-left: -40px;
    }
</style>
<body>
    <p>You should see a green rectangle with a black border, 40px wide. You should see no red.</p>

    <div class="container">
        <div class="flex">
            <div class="item first"></div>
            <div class="item neg-marg"></div>
            <div class="item"></div>
        </div>
    </div>
</body>