render-heading.html

<h{{ .Level }} id="{{- .Anchor | safeURL -}}" onmouseenter="this.firstElementChild.style.visibility='visible';"  onmouseleave="this.firstElementChild.style.visibility='hidden';">{{ .Text | safeHTML }}
<a class="header-link" href="#{{ .Anchor | safeURL }}" style="visibility: hidden;"><svg xmlns="http://www.w3.org/2000/svg" fill="currentColor" width="24" height="24" viewBox="0 0 24 24"><path d="M0 0h24v24H0z" fill="none"/><path d="M3.9 12c0-1.71 1.39-3.1 3.1-3.1h4V7H7c-2.76 0-5 2.24-5 5s2.24 5 5 5h4v-1.9H7c-1.71 0-3.1-1.39-3.1-3.1zM8 13h8v-2H8v2zm9-6h-4v1.9h4c1.71 0 3.1 1.39 3.1 3.1s-1.39 3.1-3.1 3.1h-4V17h4c2.76 0 5-2.24 5-5s-2.24-5-5-5z"/></svg></a>
</h{{ .Level }}>