🐛 Fix Unsplash when using Night Shift (#828)
🐛 Fix Unsplash when using Night Shift (#828)

closes https://github.com/TryGhost/Ghost/issues/8905
- import unsplash css file in `app-dark.css`
- add background and logo styles to match night shift styles
kevinansfield/Ghost-Admin,TryGhost/Ghost-Admin,TryGhost/Ghost-Admin,acburdine/Ghost-Admin,acburdine/Ghost-Admin,kevinansfield/Ghost-Admin