FEATURE: New style for personal messages (PR #13800)

This introduces a new bubble style for personal messages

Outside of styles directly impacting the personal messages, there are some supporting additions:

  • Adds class .current-user-post to your own posts
  • Adds class .embedded-reply to embedded posts’ .topic-meta-data
  • Adds new --tertiary-very-low color
  • Reworks some styles for deleted posts

GitHub