In brief
animation-fill-mode controls animation styles before and after active playback. forwards can retain the ending effect according to direction and iteration count.
Useful to know
animation-fill-mode controls animation styles before and after active playback. forwards can retain the ending effect according to direction and iteration count. [1]
It does not rewrite the element's underlying CSS rules. Removing the animation can change the result. For a lasting interface state, model that state rather than relying only on a completed effect.
Sources
For further detail and to check the information: