Animation of the offset of a linearGradient
offset of a linearGradient is animated starting after 2s for 10s.
For comparsion a blue rectangle is animated generating a
similar visible effect. The red part of the linearGradient
is always covered completely with the blue rectangle.
Because the blue rectangle has fill-opacity 0.8, the colour
is a little bit different with the red part of the linearGradient
below is, indicating that it is painted at all.
Anyway, if something red gets visible or the blue rectangle
has the same colour inside and outside of the black box
an error is occured.