Anchor link/styles.css

a > span.anchor-visible::after {
	content: '#';
	float: left;
	margin-left: calc(-1ch - .1ch);
	padding-right: .1ch;
	-webkit-user-select: none;
	user-select: none;
	opacity: 0;
	transition: color .25s,opacity .25s;
}

/* the margin needs to be greater inside lists so it doesn't collide with the list marker */
ul a > span.anchor-visible::after {
  margin-left: calc(-3.4ch - .1ch);  
}

:hover > a > span.anchor-visible::after,
a:focus > span.anchor-visible::after {
	opacity: 1;
}

/* templatestyles appears to lack :has() support at the moment
a:has(> span.anchor-visible) {
	float:left;
}*/