If you’re not familiar with the general sibling combinator, the ~ li in li:nth-last-child(6):first-child ~ li means “any li elements that occur after li:nth-last-child(6):first-child.” In the following example, the elements each adopt a green font color if there are precisely six of them in total. Web design is about mutability, difference, uncertainty. It’s about not knowing. Uniquely, it is a mode of visual design not about manifesting a form, but about anticipating the different forms something might take.