Once you're on a challenge screen in the platform, you'll notice a range of different markings. These markings can appear on files in the file tree or in the code. Their purpose in life is to show you the files or code lines where the original vulnerability or code differences occur (when comparing).

Markings in the file tree

The files where the original vulnerability occurred are marked with a red 'X'
Files that display code differences are marked with an asterisk. *

Markings in the code view

Lines in which the original vulnerability occurs are marked with a red 'X'
Removed code is marked in red and crossed out
Added code is marked in green 

Markings in the inline code view

Removed code is marked in red with a minus (-) symbol
Added code is marked in green with a plus (+) symbol