Notification list enhancements, fix striped tables on dark theme (#24639)

- Make code block rendering via backticks work
- Remove link color unless hovered
- Remove table stripes and fix stripes rendering on dark theme for other
tables
- Introduce new `button-link` class discussed previously for buttons
that look and act like links and apply it to the two right-side buttons
- Reduce box padding by 8px on each side
- Fix "Mark all read" button margin-right
- brighten `--color-markup-code-block` on arc-green

### Before
<img width="1216" alt="Screenshot 2023-05-10 at 20 00 30"
src="66da9ec2-dd09-4ef0-8f1d-1822a18b6b43">
<img width="1211" alt="Screenshot 2023-05-10 at 20 00 48"
src="f48e30a2-9a00-4723-93aa-79b97ca0ba0c">

### After
<img width="1222" alt="Screenshot 2023-05-10 at 20 09 59"
src="c956e0d0-b3d9-42a4-a3ed-f0431c22bf3f">
<img width="1218" alt="Screenshot 2023-05-10 at 20 05 34"
src="f72c1628-3961-4c28-9263-07cdf7531316">

templates/user/dashboard/navbar.tmpl

@@ -78,7 +78,7 @@
 
 	{{if .ContextUser.IsOrganization}}
 		<div class="right stackable menu">
-			<a class="{{if .PageIsNews}}active {{end}}item" style="margin-left: auto" href="{{.ContextUser.DashboardLink}}{{if .Team}}/{{PathEscape .Team.Name}}{{end}}">
+			<a class="{{if .PageIsNews}}active {{end}}item gt-ml-auto" href="{{.ContextUser.DashboardLink}}{{if .Team}}/{{PathEscape .Team.Name}}{{end}}">
 				{{svg "octicon-rss"}}&nbsp;{{.locale.Tr "activities"}}
 			</a>
 			{{if not .UnitIssuesGlobalDisabled}}