app/src/components/Reference.astro

---
interface Props {
    /** Unique ID for the reference */
    id: string;
    /** HTML caption for the reference */
    caption: string;
}

const { id, caption } = Astro.props as Props;
---

<div class="reference-wrapper" id={id}>
    <figure class="reference">
        <div class="reference__content">
            <slot />
        </div>
        <figcaption class="reference__caption" set:html={caption} />
    </figure>
</div>

<style>
    .reference-wrapper {
        margin: var(--block-spacing-y) 0;
    }

    .reference {
        margin: 0;
    }

    .reference__content {
        /* Content can be anything */
    }

    .reference__caption {
        text-align: left;
        font-size: 0.9rem;
        color: var(--muted-color);
        margin-top: 6px;
        background: var(--page-bg);
        position: relative;
        z-index: var(--z-elevated);
        display: block;
        width: 100%;
    }
</style>