Add easing to the portal UI

[chrisberridge]

For UI animations/transitions the portal UI utilizes .ease-linear which makes things look jerky and a little rough (check out the sidebar expansion animation when a sub-nav is present).

Could we replace this as the default with this Tailwind CSS easing function (or equivalent)?

ease-[cubic-bezier(0.25,0.1,0.25,1)]

See https://www.shadcn.io/easings for reference.