What geometry theorem is dynamically being illustrated in the animation below? [br](Feel free to move the BIG WHITE POINTS anywhere you'd like!)
[b]Theorem:[/b][br][br]If a quadrilateral is a parallelogram, then it has both pairs of opposite angles congruent.
Describe the steps animated in the diagram above:
1. Two sides of Parallelogram are drawn[br]2. Corresponding angles of parallel lines are drawn[br]3. Pink Vertical angles are drawn [br]4. Supplementary Angles are Drawn [br]5. Opposite angles are shown to be congruent.