ant-design/style/components/dropdown.less

@dropdownPrefixCls: rc-dropdown;

.@{dropdownPrefixCls} {
  position: absolute;
  left: -9999px;
  top: -9999px;
  z-index: 1070;
  display: block;
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  font-size: 12px;
  font-weight: normal;
  line-height: 1.5;
  padding-top: 7px;

  &-menu {
    outline: none;
    position: relative;
    list-style-type: none;
    padding: 0;
    margin: 2px 0 0 0;
    text-align: left;
    background-color: #fff;
    border-radius: 3px;
    box-shadow: 0 1px 5px #ccc;
    background-clip: padding-box;
    border: 1px solid #ccc;

    > li {
      margin: 0;
      padding: 0;
    }

    &:before {
      content: "";
      position: absolute;
      top: -4px;
      left: 0;
      width: 100%;
      height: 4px;
      background: rgb(255, 255, 255);
      background: rgba(255, 255, 255, 0.01);
    }

    & > &-item {
      padding: 7px 10px;
      clear: both;
      font-size: 12px;
      font-weight: normal;
      color: #666666;
      white-space: nowrap;

      &:hover {
        background-color: #ebfaff;
      }

      &-disabled {
        color: #ccc;
        cursor: not-allowed;
        pointer-events: none;

        &:hover {
          color: #ccc;
          background-color: #fff;
          cursor: not-allowed;
        }
      }

      &:last-child {
        border-bottom-left-radius: 3px;
        border-bottom-right-radius: 3px;
      }

      &:first-child {
        border-top-left-radius: 3px;
        border-top-right-radius: 3px;
      }

      &-divider {
        height: 1px;
        margin: 1px 0;
        overflow: hidden;
        background-color: #e5e5e5;
        line-height: 0;
      }
    }
  }

  .effect() {
    animation-duration: 0.3s;
    animation-fill-mode: both;
    transform-origin: 0 0;
  }

  &-slide-up-enter {
    .effect();
    opacity: 0;
    animation-timing-function: cubic-bezier(0.08, 0.82, 0.17, 1);
    animation-play-state: paused;
  }

  &-slide-up-leave {
    .effect();
    opacity: 1;
    animation-timing-function: cubic-bezier(0.6, 0.04, 0.98, 0.34);
    animation-play-state: paused;
  }

  &-slide-up-enter&-slide-up-enter-active {
    animation-name: rcDropdownSlideUpIn;
    animation-play-state: running;
  }

  &-slide-up-leave&-slide-up-leave-active {
    animation-name: rcDropdownSlideUpOut;
    animation-play-state: running;
  }

  @keyframes rcDropdownSlideUpIn {
    0% {
      opacity: 0;
      transform-origin: 0% 0%;
      transform: scaleY(0);
    }
    100% {
      opacity: 1;
      transform-origin: 0% 0%;
      transform: scaleY(1);
    }
  }
  @keyframes rcDropdownSlideUpOut {
    0% {
      opacity: 1;
      transform-origin: 0% 0%;
      transform: scaleY(1);
    }
    100% {
      opacity: 0;
      transform-origin: 0% 0%;
      transform: scaleY(0);
    }
  }
}