How to hide buttons in the mobile chat menu?

You may hide buttons in the mobile menu view.

Hide Full Screen button
.opt-full-screen { display: none; }

Hide QR code buttons
.qr-li { display: none; }

Hide small size fonts button
.opt-sm-font { display: none; }

Hide big font button
.opt-big-font { display: none; }

Hide pin the position button
.pin-li { display: none; }

Hide sound on/off button
.sound-li { display: none; }

To know how to edit the mobile CSS, refer to this link.