The win conditions for many of the challenges are inconsistent and frustrating. Throughout the early stages (Level 1), the required syntax for margin and padding can sometimes be accepted with or without spaces after the colon as well as requiring the long string instead of accepting the specific side version that the instructions lead you to believe is the right parameter to change.
padding: 10px 0 0 0;
Later on, around level 4, the instructions for margin and padding start to mix up their directive phrases. Where "add space below X element" has indicated the margin parameter before, the win condition is now requiring padding. I'm fine with using descriptive words to try to indicate which parameter to adjust, I think it helps with critical thinking compared to just straight up telling which parameter to use in the instructions, but I would ask for consistency throughout.
Unfortunately there were too many instances of both issues for me to document each. I think a general review of the wording and win conditions for the challenges in this course with these issues in mind is in order.
Edit: There appears to be an issue with the win condition script where, using a hexidec color in the background: parameter will not consistently register. This appears several times throughout 4.11 and 4.12. Even after copying the answer, the win condition will not be met, stating that "You didn't set the right background color for the (class)". I've found that repeatedly pressing the "Check My Work" button will eventually make this issue go away and register the challenge step as completed.