test.cshtml

<div class="row">
    <div class="col-md-4 text-danger bg-black p-3">
        <p>The document is rendered as HTML next to this box.</p>
    </div>
    <div class="col-md-8">
            <template shadowrootmode="open">
                @Html.Raw(ViewBag.Document)

                <style>

                    :host > p {
                        /*font-family: Arial, sans-serif !important;*/
                    }

                    .Style1 {
                        color: red;
                    }

                </style>

            </template>
    </div>
</div>