Improve styles of Now view

Follow up to #1237

Animate buttons when a task is completed or a new one is focused
Add back arrow button in top left
Make focus color the same color as when focusing on a task/agenda event on the day view.
Replace hard-coded colors: style(web): use tailwind to style colors and tooltips #1266 (comment)
Fix unresolved comments here: style(web): use tailwind to style colors and tooltips #1266
Update shortcuts overlay
add tooltip when hovering over now buttons

Closing, as the now view was removed in #1850

Navigation Menu