Improve screenshot in Passkey section

[edalzell]

The screenshot in the Passkey section (https://statamic.dev/control-panel/users#passkeys) isn't very legible:

Or maybe not make it so dark? hard to tell what we're looking at.

[jasonvarga]

That's supposed to be highlighting the specific part of the page but I agree it's a little much. I didn't realize it was dim at first - I thought it was all black.