vant/packages/vant-css/src/popup.css

.van {
  &-modal {
    position: fixed;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    background-color: rgba(0, 0, 0, 0.701961);
    transition: all .5s ease-out;
  }

  &-popup {
    position: fixed;
    background-color: #fff;
    top: 50%;
    left: 50%;
    transform: translate3d(-50%, -50%, 0);
    backface-visibility: hidden;
    transition: .2s ease-out;

    &--top {
      width: 100%;
      top: 0;
      right: auto;
      bottom: auto;
      left: 50%;
      transform: translate3d(-50%, 0, 0);
    }

    &--right {
      top: 50%;
      right: 0;
      bottom: auto;
      left: auto;
      transform: translate3d(0, -50%, 0);
    }

    &--bottom {
      width: 100%;
      top: auto;
      bottom: 0;
      right: auto;
      left: 50%;
      transform: translate3d(-50%, 0, 0);
    }

    &--left {
      top: 50%;
      right: auto;
      bottom: auto;
      left: 0;
      transform: translate3d(0, -50%, 0);
    }
  }
}

.popup-slide-top-enter,
.popup-slide-top-leave-active {
  transform: translate3d(-50%, -100%, 0);
}

.popup-slide-right-enter,
.popup-slide-right-leave-active {
  transform: translate3d(100%, -50%, 0);
}

.popup-slide-bottom-enter,
.popup-slide-bottom-leave-active {
  transform: translate3d(-50%, 100%, 0);
}

.popup-slide-left-enter, .popup-slide-left-leave-active {
  transform: translate3d(-100%, -50%, 0);
}

.popup-fade-enter, .popup-fade-leave-active {
  opacity: 0;
}