What do you mean how to collapse? Which screen is this?
Who is the designer of this side bar? Please teach me how to collapse..

I've never seen this layout before and I use my Android tablet and the Chess.com website on my desktop. Is this the new update?

Oh I see what your asking. I was thinking about the Chess.com app which has a different layout. Android users can access this layout if they connect to Chess.com though the website. To my knowledge there is not a collapse or extend option if you are using an Android. This option exists only if your on a desktop/laptop.

If you still can't understand, follow this step.
1. Take your android device.
2. Open Chrome Browser.
3. Open option
4. Check 'desktop site'
5. Click on address bar.
6. Type chess.com.
7. enter..
Now see and increase your knowledge.
*If you can't understand my word, I will send you screenshots.

Hello Ahmed,
I have followed your instructions. I have opened the Chess.com desktop site on my Android tablet and Android phone using Chrome and I am not getting the layout your getting. The layout I am getting is quite similar to the desktop layout you would see when you login to Chess.com on a regular desktop computer. Why not try logging in to Chess.com's desktop site from a different server like Google or Firefox instead of Chrome? I'm sorry I couldn't help.
Good Luck
In my Android chrome, what I use most, found that I can't collapse your new side menubar. Who is the designer of this???
Tell me how to collapse this.
Nowadays I don't browse your website much. Mostly play on apps. If you don't care your users, soon I might have to stop browsing chess.com!