Selectors needed a lot of explaining

[projectgus]

CSS selectors needed a lot of explaining, it usually took a few questions/answers with a coach for people to understand. They're mostly introduced in the first portfolio chapter but would benefit from more detail.

This could be a good candidate for some question/answer "given these HTML elements, how would you apply a colour to just the headings, how about just the second heading, how about just the third and fourth headings?" type questions. We could use the same "Show Solution" pattern that is in some of the Python workshops.