I built a basic HTML & CSS website using a lot of HTML core features, such as ordered and unordered lists, parent-child relationship, descendant elements and ancestors, HTML layouts. I also used some CSS core concepts, like cascading, inheritance and specificity, the CSS box model, the different selectors, combinators, classes and IDs, block and inline elements, vertical margins and padding to inline elements, vertical margins limitations exceptions for replaced inline elements, margin collapsing.
