Sidebar rmmoval?

from the codding of sidebar.php, it should disappear when you have all widgets removed from ‘appearance – widgets’ area.
unfortunately, this is not carried through into changing the layout, for example by changing the body_class as a basis for a CSS applied to ‘no-sidebar’ situations.

you can fix that with some coding:

example:
in a child theme, add this into functions.php:

add_filter( 'body_class', 'no_sidebar_class' );
function no_sidebar_class( $classes ) {
	if (   ! is_active_sidebar( 'sidebar-1' ) ) $classes[] = 'no-sidebar';
	return $classes;
}

then add this into style.css of the child theme:

.no-sidebar .column.two-thirds { width: 100%; }