Minor CSS tweak.
I really need someone with more solid CSS experience to help me dress this up a bit.
The position and display of the checkboxes is a bit awkward.  In order to use simplified JS, I chose the 'easy' route and included the <input> within each Chart DIV.  But that means they ride along in position too, which leads to this awkward behavior.
Ideally, I should separate the selectors from the chart and be able to style that block independently; elsewhere on the screen.