Bug: Fix AlertList styling

[ashharrison90]

• as part of Chore: Migrate more SCSS grafana#90224, i removed these SCSS styles from core grafana
  • unfortunately the dashboard i was using to see which plugins were using which styles never flagged this plugin as using them 😭
  • still need to dig into how and why these usages weren't shown
• copy these styles into the plugin where they can be controlled and adjusted at your leisure 😄

thanks to @PedroRibas13 @mplm17 for raising this 🙇

Fixes #1868

[zoltanbedi]

Thanks for fixing this for us @ashharrison90 🫶