Use #site-navigation instead of #site-links so that siblings also

get the updated outline.

Also remove the `list-group-item` outer selector.  Just make the focused
`.nav-link` have the elevated `z-index` so that the outline doesn't go
under the active link when the `.nav-link` before it is focused in the
siblings..

htdocs/themes/math4-yellow/_theme-overrides.scss

@@ -29,3 +29,7 @@ a:not(.btn):focus {
 	--ww-site-nav-link-active-background-color: #{$primary};
 	--ww-site-nav-link-active-color: #{color-contrast($primary)};
 }
+
+#site-navigation a:not(.btn):focus {
+	outline-width: 2px;
+}

htdocs/themes/math4/bootstrap.scss

@@ -98,7 +98,7 @@ a:not(.btn):focus {
 	outline-width: 1px;
 }
 
-#site-links a:not(.btn):focus {
+#site-navigation a:not(.btn):focus {
 	outline-width: 2px;
 }
 

htdocs/themes/math4/math4.scss

@@ -219,11 +219,10 @@ $site-nav-width: 250px !default;
 
 				}
 			}
-			&.list-group-item {
-				.nav-link:focus {
-					position: relative;
-					z-index: 2;
-				}
+
+			.nav-link:focus {
+				position: relative;
+				z-index: 2;
 			}
 		}
 	}