CI3 User Guide Style

Good job but I'm also miss the complete doc overview like Peterdenk said.

Personally think it's faster to search specific topic using CTRL + F from the full table of contents than waiting the search box to roam in the entire database/directories and display results slowly on the page. Or by clicking multiple times few level down from the navigation link on the left. I think there are way too many clickings compare to previous doc.

The current one is nice but it's good if can keep the previous slide down full overview table of contents.