CSS variables for arrowhead - dark/light theme
CSS variables for arrowhead - dark/light theme

Signed-off-by: Itay Dafna <2d6a3cece74cbf11efbcb3084048dd05c1a48684@gmail.com>

bloomberg/bqplot,bloomberg/bqplot,ChakriCherukuri/bqplot,ChakriCherukuri/bqplot,bloomberg/bqplot,ChakriCherukuri/bqplot