[Tails-ux] Highlighting colour uniformity and visibility

So the cursor hover highlighting in Tails 4.0 is problematic, I think.
The problems are (1) consistency, and (2) visibility.

Visibility: The colour used to highlight sidebar entries in the Settings
app as the mouse cursor hovers over them is very subtle, light grey on
white background. The highlight colour for the menus in the setting app
are actually worse, so subtle that I can't even see it unless I focus -
a good example is the drop-down menu available on the Wi-Fi pane, which
is white highlight on a very light grey background.

Consistency: So, the highlighting colour on hover for the menu options
in Thunderbird is a nice bold blue. But the highlighting colour for the
Settings app is different (see above). Also, the highlighting colour for
TorBrowser menus is also different, also grey but seems slightly darker
than the settings app grey.

The biggest problem for me is the visibility, but the consistency is
also an issue. Could the highlighting be applied uniformly in all apps
as the bold blue used in Thunderbird? I think that works well.