warning: The Sugarcane (and Jonah & Responsive) story format stopped being maintained in mid 2015 and since then some web-browser have changed the functionality allowed to locally run HTML files. One of the story format's features effected by these changes is it's ability to save the Reader's progress.
I strongly suggest you change your story to use the SugarCube 2.x story format instead, doing so has the added advantage of giving your story a more robust Save system and it comes with the built-in ability of being able to toggle the display of it's left sidebar.
...to close the sidebar...
What exactly do you mean by this?
a. Hide the side bar completely so that it never appears for the life cycle of the story.
b. Using TwineScript within your Passage content to toggle the displaying of the side bar as needed.
c. Allow the Reader to toggle the displaying of the side-bar.
d. A combination of b & c.