istio.io/layouts/shortcodes/warning.html

<div class="callout warning">
    <div class="type">
        <svg class="large-icon"><use xlink:href="/img/icons.svg#callout-warning"/></svg>
    </div>
    <div class="content">
        {{ $trimmed := trim .Inner " \n" }}
        {{ markdownify $trimmed }}
    </div>
</div>