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Below are some hints that you may find useful when using the Documentation theme.
The Confluence documentation uses the Documentation theme. If you are reading this documentation online on the Atlassian documentation wiki, you are seeing a working version of the Documentation theme.
The theme constructs the page tree in the left-hand panel from all pages that are child pages of the space’s home page. Each space has a single page designated as the 'Home' page. You can specify the home page in the space administration section.
Cause 1: Your pages are not under the space's home page. The most probable reason why your pages do not appear in the page tree in the left-hand panel is this: The theme constructs that table of contents from all pages that are child pages of the space’s home page. If your pages are above the home page in the page tree, they will not appear in the left-hand panel.
There are two ways to fix the problem:
Cause 2: Problem with upgrade from Confluence 3.1, with Documentation theme as plugin, to Confluence 3.2 or later with Documentation theme bundled. If your existing Confluence installation already has the Documentation theme plugin installed, you may find that after upgrading to Confluence 3.2 the left-hand navigation bar is empty in the spaces that use the theme. The fix is to enable all modules of the Documentation theme plugin. See the knowledge base article.
If your entire left-hand panel has disappeared when using the Documentation theme, this is probably because you have clicked the sidebar icon at top right, next to the search box. Click the icon again to restore the panel.
The Confluence user interface does not offer a way to change the default width of the left-hand navigation panel supplied by the Documentation theme. Users can change the width by dragging the middle bar, but the default width is not configurable. This post on Atlassian Answers gives a way to do it with CSS: Documentation Theme - Default Width (in px) of left panel.