@acer 

I had tried something similar which worked fine but gave me troubles when trying to plot a polygon on top e.g.

display(
polygon([[0,1],[1/2,-sqrt(15)/4],[-1/2,-sqrt(15)/4],[0,1]],color=blue,style = line,thickness=4,transparency=0),
ellipse([0, 0], 2, 1, filled=true, color = red, style=polygon),
ellipse([0, 0], 2, 1, thickness=2, color = red, style=line),
size=[1000,500],scaling=constrained,axes=none);
 

replacing "thickness=2" with "filled=true" solves this problem :)

I wouldn't have come up with this myself as it seems contradicting to use filled if you want line style.