Simplify the chart definition based on the tutorial
Switch to SVG for the graphs.

Provides more flexibility
Remove the magic number for the chart height
Make the text white again.

The tutorial was missing details on how to do this step though, so I
just winged it. :-)
Add some padding to the chart
add some unstyled reference lines for the chart
Fix up the text styling
Finish up the tutorial

Fix up the lines so they're behind the bars. It looks better this way.
Add a solid dark line for the Y axis. Also add text values for the
reference points at the top