Changes from @tanya

#9 "that exist"

#17 list them

#22 "we opened earlier" - maybe just intro Codepen here instead of at
the start?

#25 line wrapping on smaller screen

#26 "makes your HTML more human-readable"

#31 input not shown in preview

#53 only focus on pixels for today

#66 "A block container"

#67 nav should contain links cos we have covered them

#68 "to indicate"

#71 "mentors" rather than "volunteers"

#73 "To create a standard..."

#81 "properties"

#82 "mentors"