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

.@{prefixCalendarClass}-picker .@{prefixCalendarClass},
.@{prefixCalendarClass}-picker-container .@{prefixCalendarClass} {
  position: absolute;
  display: none;
  left: -9999px;
  top: -9999px;
  z-index: 9;
}

.@{prefixCalendarClass}-picker {
  position: relative;
  display: inline-block;

  &-icon {
    position: absolute;
    -webkit-user-select: none;
    user-select: none;
    .transition(all .3s @ease-in-out);
    width: 14px;
    height: 14px;
    line-height: 14px;
    right: 8px;
    color: #999;
    top: 50%;
    margin-top: -7px;
    &:after {
      content: "\e60c";
      font-family: "anticon";
      font-size: 14px;
      color: #999;
    }
  }
  &-open .@{prefixCalendarClass},
  &-container-open .@{prefixCalendarClass} {
    display: block;
  }
  &-open &-input {
    border-color: @input-focus-border-color;
    outline: 0;
    box-shadow: 0 0 3px tint(@input-focus-border-color, 20%);
  }
}