Only puzzle without left and top menu

Hello!
Is it possible to display only the daily puzzle on the browser screen so that the child does not have the chance to randomly or specifically follow the link to another place?
Only puzzle lichess.org/training/daily without left and top menu.

Example: ibb.co/Y311Cqd

You can achieve this with userstyles, e.g. using Stylus, and this CSS:
#site_header, #top {display:none;}

Thanks for the tip. Do I need to raise a separate web server, or can this be implemented, for example, by adding a script in the browser?

I find firefox addon STYLISH. Thanks.
I will sort this out.

There are privacy concerns with Stylish:
robertheaton.com/2018/07/02/stylish-browser-extension-steals-your-internet-history/

Use Stylus instead: addons.mozilla.org/en-US/firefox/addon/styl-us/

Yes. Don't use Stylish. Use Stylus.

Thank! Install Stylus. It turned out to remove the top and left menu. Only the board is displayed. Now I suffer to make a board on the whole screen. I can not figure it out yet.

Can't you just change the board size?
username --> Board geometry --> Board size
and then enable userstyle

Thank! I saw it, but is it possible to do it somehow programmatically without user intervention? I tried different transform combinations: scale (x, y); transform-origin: 0 0; ... but after the first move of any piece, everything starts to be displayed incorrectly, some script is used to know there. Checked in both chrome and firefox.

Perhaps something like this:

.lichess_game .cg-board-wrap { width:768px !important; height:768px !important; }
.underboard .center { width:768px !important; }
div.lichess_game { height:768px !important; }
body>div.content { width: 1280px !important; }

You may need to adjust the values a bit and also reload the page after you enable styles.