Is anyone else having this issue in Safari even with fresh installs? There's a noticeable delay when hovering over buttons/links (like the side bar links), opening dropdowns, using addons like the ColorPicker, and even typing in textareas. Problem goes away in Chrome, and isn't present on other webapps/sites. Seems like an issue with javascript / css, there's a large hiccup when scrolling down on an Entry page when the header gets 'stuck' to the top of the window.

The issue seems to go away if the window is resized to mobile (where the side nav bar is hidden) or when the nav bar is set to display: none. This leads me to believe it is some css transition/javascript issue with rendering.

Edit: It doesn't happen on control panel pages with less content: like the Dashboard or Pages page. It happens on any pages that have a lot of content and therefore scrolling. Like editing fieldsets or editing an Entry with enough fields that the page scrolls. As soon as there is a lot of content on a control panel page, the entire cp crawls to a halt, sidebar becomes less responsive, fieldsets are slow to respond (like Select).

This didn't seem to be an issue before the recent control panel redesign...

Edit: I have tried it on Sierra and High Sierra, tried with a completely reset browser no plugins or extensions, in a local dev environment with fresh install, and a long-running live site. Using a 15" retina mbp display at full width.

To reproduce, use Safari on a mac at full 15" width; create a page with a handful of fieldsets, and on the page with fieldsets or even while editing fieldsets through the CP try and hover over sidebar nav-links. You will notice how unresponsive and laggy the hover-states are compared to on a dashboard or shorter page. This carries through to opening Select fields and many controls.