The activity indicator was inheriting the default white color in dark

mode, which clashed with the hard-coded yellow on the indicator. The

look was also very dated in general.
We now use our Ink light color palette for the background, and the

on-light colors for the text and links, giving a consistent appearance

between light and dark modes. This particularly stands out well on dark

mode.
The appearance has also changed to be more of a pill shape with

consistent, flexible spacing, slightly offset from the top. This

replaces the docked fixed-size rectangle we had from the olden days.

Tested loading/saving indicators and the server error display on both

light and dark modes.