Main Theme

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The Main Theme - this is a full with Theme, hence content placement is partly based on the size of the users screen.

Acceptable as external site

Documentation Theme

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The Documentation Theme - this is a full with Theme, hence content placement is partly based on the size of the users screen.

General not very acceptable as external site, unless documentation is the main requirement.

This sidebar can be configured as a page, which adds flexability a lot, se Placing Resources for ideas of placing the sidebar page.

Easy Reader Theme

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The Easy Reader Theme - this is a fixed with Theme, hence content placement is pretty controlabledcontrolable, making it my favorite as an external site.

Review CSS For Confluence 4.X for setting the width.