ant-design/style/components/datepicker/Picker.less

.@{calendar-prefix-cls}-picker-container {
  position: absolute;
  z-index: 1070;

  &.slide-up-enter.slide-up-enter-active&-placement-topLeft,
  &.slide-up-enter.slide-up-enter-active&-placement-topRight,
  &.slide-up-appear.slide-up-appear-active&-placement-topLeft,
  &.slide-up-appear.slide-up-appear-active&-placement-topRight {
    animation-name: antSlideDownIn;
  }

  &.slide-up-enter.slide-up-enter-active&-placement-bottomLeft,
  &.slide-up-enter.slide-up-enter-active&-placement-bottomRight,
  &.slide-up-appear.slide-up-appear-active&-placement-bottomLeft,
  &.slide-up-appear.slide-up-appear-active&-placement-bottomRight {
    animation-name: antSlideUpIn;
  }

  &.slide-up-leave.slide-up-leave-active&-placement-topLeft,
  &.slide-up-leave.slide-up-leave-active&-placement-topRight {
    animation-name: antSlideDownOut;
  }

  &.slide-up-leave.slide-up-leave-active&-placement-bottomLeft,
  &.slide-up-leave.slide-up-leave-active&-placement-bottomRight {
    animation-name: antSlideUpOut;
  }
}

.@{calendar-prefix-cls}-picker {
  position: relative;
  display: inline-block;
  outline: none;
  font-size: @font-size-base;
  transition: opacity 0.3s ease;

  > input {
    outline: none;
  }

  &-open > span:first-child {
    transition: opacity 0.3s ease;
    opacity: 0;
  }

  &-icon {
    position: absolute;
    user-select: none;
    .transition(all .3s @ease-in-out);
    width: 12px;
    height: 12px;
    line-height: 12px;
    right: 8px;
    color: #999;
    top: 50%;
    margin-top: -6px;
    &:after {
      content: "\e654";
      font-family: "anticon";
      font-size: 12px;
      color: #999;
      display: inline-block;
      line-height: 1;
      vertical-align: bottom;
    }
  }
}