The current entry of vertical menus is only marked by a barely visible color and is not announced to screen readers

The vertical menus generated by the #verticalNavigation macro, used by the syntax guide and by the user profile menu, mark the current item and the current group only with a background color:

• The current item gets component-active-bg, which the Iceberg color theme maps to list-group-hover-bg (#f5f5f5 on white, a contrast ratio of about 1.1:1).
• The current group header gets a slightly darker blue (#2f6ead instead of #3E79BC, about 1.2:1).

So:

• Sighted users can hardly tell which entry is the current one, and color alone conveys that information (WCAG 1.4.1 Use of Color, 1.4.11 Non-text Contrast).
• Screen reader users are not told at all, since the markup sets no aria-current attribute on the current entry (WCAG 1.3.1 Info and Relationships).

Steps to reproduce

1. Open the syntax guide and select a section, e.g. Headings.
2. Look at the menu entry of that section, and inspect it.

Expected

The current entry is marked with aria-current="page", or aria-current="true" for a group, and its visual indication does not rely on a barely visible background color, e.g. a bolder font or a left border with enough contrast.

Actual

Only a near-invisible background color marks it.

This is not a regression: it was the same before XWIKI-23673 converted vertical-menus.less to CSS.