SSO: Tooltip and tooltip textbox display enhancements for consistency and greater accessibility

### Impacted plugin

Jetpack

### What

SSO tooltip texboxes should have no visibility issues (making them more accessible), and tooltips consistent

### How

The textboxes themselves should ideally have a more obviously different background color or a border if possible - something to help differentiate between the backgound color and the text box itself.

The tooltip icons, if possible, would ideally be the same.

Steps to replicate:

* Start with a site that's connected to WordPress.com, and where you have activated the SSO feature under Jetpack > Settings > Security
* Go to Users > All Users in your dashboard.
* Make sure you have at least 2 users, one of which has not been invited to join WordPress.com when creating the user.

Current display:

This was suggested in internal testing: p8oabR-1wt-p2#comment-8015

Reproduce the SSO tooltip display in Jetpack by following the Users > All Users steps after enabling SSO under Jetpack > Settings > Security. Compare the textbox and tooltip icon against the reported screenshot; done means the textbox is visibly distinct from its background and the tooltip icons are consistent.

Written by the indexing model from the issue text.