- Remove a semantically incorrect `<button>` wrapping the loading
   spinner and a redundant wrapping `<span>`.
 - Vertically center the spinner by adding a wrapper `<div>` in the
   spinner component itself, so that there is less of a visual shift
   when switching between displaying the loading indicator and the
   search bar.
 - Add a meaningful title attribute to the spinner. Properly indicating
   when the sidebar's content is changing/being loaded to ATs requires
   additional work which is not tackled here.