wrong class for no sidebars at _layout--grid.sass

At _layout--grid.sass you get:

#content
  .no-sidebars &
    // 100% width for small screens.
    @include fill-parent

But you should get:

#content
  .no-sidebar &
    // 100% width for small screens.
    @include fill-parent

to suit this line at html.html.twig template:
(not sidebar_first and not sidebar_second) ? 'no-sidebar',

Adding patch here...