You typically find the solution in the same folder as the starting code on GitHub. It’s often in a file called “marking.md”. Sometimes for bigger exercises there is a separate folder next to the starting code folder called “assessmentName-finished” (or similar). For this exercise it’s here: https://github.com/mdn/css-examples/blob/main/learn/tasks/selectors/marking.md
I recommend looking for a specific selector on MDN when it’s not clear what it’s doing. For example: ::first-line (:first-line).
I’m happy to help you further if you have some specific questions.