
item {
    display: block;
    background-color: green;
    width: 50px;
    height: 50px;
    margin-inline-start: 10px;
}
</style>
</head>
<body>
    <flexbox class="initial-margin-trim" id="to-no-margin-trim">
        <item></item>
    </flexbox>
    <flexbox id="to-margin-trim">
        <item></item>
    </flexbox>
</body>
<script>
document.body.offsetHeight;
document.getElementById("to-no-margin-trim").style["margin-trim"] = "none";
document.getElementById("to-margin-trim").style["margin-trim"] = "inl