We've been working on some layout changes to the Shopify web admin.
Last week, we shipped a change that removed the fixed black header along the top of the page. We moved all of the actions that were in that header to the sidebar. Stripping away the header helped to provide more focus on our top-level actions (based on our testing, users were able to find these actions faster and more often).
Today, we're updating the colours to increase contrast between the sidebar and your actual store content.
We'll be rolling out this new layout this afternoon.