Fine-tune spacing between cards about atypicality

[colinmorris]

A couple things worth trying on mobile:

1. splitting some of the longer cards up (e.g. the valence explainer)
2. having cards activate much earlier (to take advantage of the blank space below the chart)
3. giving songs more room to breathe. i.e. when switching to a new song (or a new contrast), delay the appearance of the first card that talks about it (give the reader an opportunity to form an impression before telling them what to think). (Restyling the year headings might help with this too)

[colinmorris]

I've pushed some changes that address 1 and 2 above. I think the situation is improved now.

May want to revisit this eventually though (in particular, number 3 above).