@Gapolyglot You’re not the only one. There’s a longer thread about the refresh here: New Admin Visual Refresh issues . Nobody has found a setting yet to move Sidekick or change the sidebar colour, but people there shared a browser CSS workaround that hides the Sidekick bar.
On the notify-customer worry, here’s a quick way to be sure: after you fulfil, scroll down to the order’s timeline. If the customer was notified, you’ll see an entry saying the shipping confirmation email was sent to their address. If it isn’t there, you can resend it from the timeline instead of redoing the fulfilment.