What is the 'hell was embittered' part of the Paschal homily?

Christ is risen. Hell was embittered when it encountered him in the lower regions. It was embittered, for it was abolished. It was embittered, for it was mocked. It was embittered, for it was slain. It was embittered, for it was overthrown. It was embittered, for it was fettered and chained. It took a body and met God face to face. It took earth and encountered heaven. It took that which was seen and fell upon the unseen. Christ is risen.