 {
      0% {
        z-index: 1; /* start behind other card */
        transform: scale(0.9);
      }
      50% {
        transform: translateX(var(--swing));
      }
      100% {
        z-index: 2; /* end in front of other card */
        transform: translateX(var(--overlap)) scale(1.1);
      }
    }

    /* when a radio button is set, swing the opposite card backwards */
    #happy-radio:checked ~ .selector .lovers-card,
    #lovers-radio:checked ~ .selector .happy-card {
      animation-name: swing-ba