ant-design/components/date-picker/style/MonthPanel.less

.@{calendar-prefix-cls}-month-panel {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  z-index: @zindex-picker-panel;
  background: @component-background;
  border-radius: @border-radius-base;
  outline: none;

  > div {
    display: flex;
    flex-direction: column;
    // TODO: this is a useless wrapper, and we need to remove it in rc-calendar
    height: 100%;
  }
}

.@{calendar-prefix-cls}-month-panel-hidden {
  display: none;
}

.@{calendar-prefix-cls}-month-panel-header {
  .calendarPanelHeader(~'@{calendar-prefix-cls}-month-panel');
  position: relative;
}

.@{calendar-prefix-cls}-month-panel-body {
  flex: 1;
}

.@{calendar-prefix-cls}-month-panel-footer {
  border-top: @border-width-base @border-style-base @border-color-split;
  .@{calendar-prefix-cls}-footer-extra {
    padding: 0 12px;
  }
}

.@{calendar-prefix-cls}-month-panel-table {
  width: 100%;
  height: 100%;
  table-layout: fixed;
  border-collapse: separate;
}

.@{calendar-prefix-cls}-month-panel-selected-cell .@{calendar-prefix-cls}-month-panel-month {
  color: @text-color-inverse;
  background: @primary-color;

  &:hover {
    color: @text-color-inverse;
    background: @primary-color;
  }
}

.@{calendar-prefix-cls}-month-panel-cell {
  text-align: center;

  &-disabled .@{calendar-prefix-cls}-month-panel-month {
    &,
    &:hover {
      color: @disabled-color;
      background: @disabled-bg;
      cursor: not-allowed;
    }
  }
}

.@{calendar-prefix-cls}-month-panel-month {
  display: inline-block;
  height: 24px;
  margin: 0 auto;
  padding: 0 8px;
  color: @text-color;
  line-height: 24px;
  text-align: center;
  background: transparent;
  border-radius: @border-radius-sm;
  transition: background 0.3s ease;

  &:hover {
    background: @item-hover-bg;
    cursor: pointer;
  }
}