Stylus extension is now recommended over Stylish (privacy concerns).

to run this, need to install tampermonkey, on chrome/firefox.

interesting. I tried this, it works but i can't click the same button to unhide it. useful if it can hide by default too.

I still needed this script, because simply hiding using, #sidebar { display:none !important; } , the content width will be shrinked too small, when the window width is reduced. (Eg. I put my monitor in portrait mode, and maximise the window)

i edited the width of the #mainbar to 50%. My requirement is to keep the default content width setting. But when I reduce the size of the window width, it should still to stay the same width.