Improve highlighted selected block in List View

[talldan]

Is your feature request related to a problem? Please describe.
As mentioned on #24609, it's quite easy to mistake the selected block for the one that has the focus ring in list view:

Here, the blue border is the focus ring, and the icon with the black background is the selected block.

Describe the solution you'd like
Make the selected block state stronger or more visible. The icon background is very subtle.

[talldan]

This may be something being tackled in #24419. @shaunandrews what do you think ... Can I close this in favor of your issue?

[talldan]

Ah yep, I see there are some designs in this comment #24029 (comment). I'll close this issue in that case.