<!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="block-start margin of item should be trimmed">
<style>
container {
    display: block;
    margin-trim: block;
    border: 1px solid black;
    margin-block-start: 10px;
}
item {
    display: block;
    inline-size: 50px;
    block-size: 50px;
    background-color: green;
}
.collapsed {
    margin-block: 50px;
    block-size: 0px
}
</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('item')">
    <container>
        <item style="margin-top: 30px;" data-expected-margin-top="0"></item>
    </container>
</body>
</html>
