wiki: no visual differentiation between active page and directories
gitlab-ce~2278648
### 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
issue