Animation-fill-mode defines how styles are applied to the target of your CSS animations outside of the animation itself. By default your CSS animations won’t affect the element you’re animating until the first keyframe is “played”, then stops affecting it once the last keyframe has completed. This can leave you with some awkward jumps and cuts. It’s not pretty. You can use animation-fill-mode to smooth these out without having to write extra CSS to match your first or last keyframe styles.