dark mode glossary popup links invisible

the element has the following style:
```css
a {
color: var(--color-link);
text-decoration: underline;
/* text-decoration-color: currentcolor; */
text-decoration-color: var(--color-link-underline);
}
```
and color results in `#F9FCFF`

element is:
```html
OU
```
(which could be a relative link, btw)

Start by inspecting the glossary popup link styles and the rendered `hxr-hoverxref hxr-tooltip reference internal` element shown in the issue, using the supplied dark-mode CSS and HTML as the reproduction. Done means glossary links are readable and visibly styled in dark mode; also verify whether the glossary URL should be relative as noted in the report.

Written by the indexing model from the issue text.