How to reduce the width of the editor in response to the question?

Can you please share a snapshot as we can’t see editor without logging in.
Regards

Hello Slavy ! 
To resolve this issue, you can try to add the following code to the style.css file:

 .wp_themeSkin table.mceToolbar {
width: 70% !important;
}
.mceLayout {
   width: 100% !important;
}
.recaptchatable {
   width: 460px !important;
}

Hope this helps !