<!DOCTYPE html>
<html>
<head>
<link rel="author" title="Sammy Gill" href="mailto:sammy.gill@apple.com">
<link rel="help" href="https://drafts.csswg.org/css-box-4/#margin-trim-block">
<meta name="assert" content="border should protect the margins inside a nested block from trimming">
<style>
.trim {
    margin-trim: block;
    outline: 1px solid blue;
}
container {
    display: block;
    width: min-content;
}
item {
    display: block;
    inline-size: 50px;
    block-size: 10px;
    background-color: green;
}
.collapsed {
    block-size: 0px;
    margin-block: 10px;
}
.border {
    block-size: auto;
    border: 10px solid black;
    margin-block-end: 25px;
}
</style>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/check-layout-th.js"></script>
</head>
<body onload="checkLayout('.collapsed')">
    <div id="target">
        <container class="trim">
            <container>
                <item></item>

                <!-- This item's block-end margin should be trimmed 
                     since it will collapse through to the outer container-->
                <container style="margin-block-end: 300px;">
                    <!-- However the margins inside this item cannot collapse through due to
                         the border and should not be trimmed -->
                    <container class="border"> 
                        <item style="margin-block-end: 20px;"></item>
                        <item data-offset-y="58" class="collapsed"></item>
                    </container>
                    <item data-offset-y="68" class="collapsed"></item>
                </container>
            </container>
            <item data-offset-y="68" class="collapsed"></item>
        </container>
    </div>
</body>
</html>
