How to resize Arc background

i would like to resize the square background of my ARC.

When you

lv_obj_set_size(myArcPtr, 80, 80 );

on the ARC object it will resize the ARC drawing aswell as the background square. I would like to be able to fully controll the background square color, size, opa etc.

How can i have acces to this object ?

This is how to ->

lv_style_set_pad_bottom(&arcStyle, LV_STATE_DEFAULT, 0);