wiki: no visual differentiation between active page and directories

~bug

Summary

In the wiki: Currently, there is no differentiation between active page (cursor) and directories. Both are black. That is confusing as the cursor is styled in the same way as directories. So you don't know what the cursor is.

steps to reproduce

1. go to https://gitlab.com/CardBook/CardBook/wikis/home
2. look at sidebar

current behavior

currently selected page ("server configuration") and directory ("servers") are both black

expected behavior

cursor and directories should be styled differently