Distinguish internal links to glossary items (black, dotted bottom
border) and sections, references and footnote (blue, dashed bottom
border).
Use darkgreen (solid bottom border) instead of blue for external links.
Signed-off-by: David Runge <dave@sleepmap.de>
Add a lightgray `background-color` for all admonition environments.
Add a palevioletred `background-color` for all admonition-warning and
warning environments.
Signed-off-by: David Runge <dave@sleepmap.de>
