I’ve revised that CSS snippet to add a delay before the tool-tip appears, so that moving your mouse across links does cause visual noise:
/* Show external link URLs on hover */
a.external-link::after {
content: attr(href);
font-size: 80%;
display: block;
position: absolute;
background-color: var(--ls-secondary-background-color);
z-index: 9999;
pointer-events: none;
padding: 0.3em 0.6em;
border-radius: 0.2em;
opacity: 0;
transition: opacity 0;
}
a.external-link:hover::after {
opacity: 1;
transition: opacity 100ms 900ms;
}