In older versions of builder the toolbar always dispayed. It's now auto-hiding when the mouse is not hovering. This class in particular (.hide-until-toolbar-hover) causes it.
When you're developing locally, at a quick glance it becomes hard to know what environment you're working on because the URL is auto-hidden when the mouse isnt hovering over it. This has added friction to the developer experience when you're compairing 2 pages side by side (local vs prod)