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Custom board theme

The only way you can modify the board and pieces is through the options in settings. when you go into live, click the gear icon and go to the board and pieces options. there's a lot of choices there.
besides those, no I don't think there's any way you could modify it to options that chess.com itself doesn't give, unless you're very tech savvy and just change the coding or something like that to show you a different board and pieces.

I made a tutorial a few days ago showing people how they can get custom pieces + board.
Just go on YouTube and search: "How To Get Custom Pieces + Custom Board on Chess.com"
My video should pop up. Hope it helps!

Use inspect element, basically right click < inspect, or otherwise press ctrl + shift + i, then navigate to the sources panel. In the sources panel, you will find a folder called themes. (Depending on your setup you may have to scroll down to see it) Click the folder to open it, then click on the script that says css?background_url. It's probably the first script in the folder. In some cases their will be two scripts in the folder, if that is so you should probably click on the first one. In the section of the script reading theme-board style image : url navigate to the right where the url is placed, and replace the url with an image of your own. If you have a file you want to upload, use or another image hosting website. Now, after you replace it you need to right click the script and click "Override content" and select folder to store overrides in. The downside of this, being, you must usually open inspect element to acticate your changes. Hope this helped.
There's no way to design your own board style.