core styling to match figma.
https://www.figma.com/file/a1nkbWgbgjRlrOY9LVurTz/Comm-%2F-Desktop-app?node-id=1170%3A77791
https://linear.app/comm/issue/ENG-530/inline-sidebar-re-style
right little content:
{F49425}
right lots of content same message grouping:
{F49428}
right image:
{F49429}
left little content:
{F49430}
left lots of content:
{F49431}
This diff needs to be landed with the entire stack.