I can't hide the side bar. I'm the administrator of the website, but I can't see user macros in the configuration. I'm very disappointed with Confluence. It is too complicated and nothing I read in the posts seem to work in my version. I'm using it hosted at Atlassian.
Can you not click the little arrows at the bottom left of the sidebar to hide it?
Using the [ key works. It's one of the handiest shortcuts I know of.
@Flavio if you hove the mouse to the middle between the sidebar and the main page, you will see a small arrow appearing. That will allow you to hide the side bar to the left side
Or if you use your mouse to hold the border blue line between sidebar and main page, and drag it to the left, you can also hide the sidebar too
I hope this help you