[Notts Police] Update styles for site messaging

[chrismytton]

Similar to the styles added for Surrey in https://github.com/mysociety/fixmystreet/commit/68cadc8ffce26523aa047c750b32c9db7945f276.

Fixes https://github.com/mysociety/societyworks/issues/4417

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.60%. Comparing base (abaded7) to head (72a1373).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## notts-police-reviewed #5068 +/- ## ====================================================== Coverage 82.60% 82.60% ====================================================== Files 394 394 Lines 30801 30801 Branches 4886 4886 ====================================================== Hits 25442 25442 Misses 3905 3905 Partials 1454 1454 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.