Bug: Incorrect Placement of Close Sidebar Button

[Undistraction]

Currently the X button to close the sidebar is located on the header. This is confusing and I would expect a button in this location to close the header, not the sidebar.

The button should be located in the sidebar and the icon should be changed to a left-facing arrow (or similar). Another option would be to display it as a kind of tab in the vertical centre of the border between sidebar and main content.