SOURCE

 .ant-select-dropdown.slide-up-appear.slide-up-appear-active.ant-select-dropdown-placement-bottomLeft, .ant-select-dropdown.slide-up-enter.slide-up-enter-active.ant-select-dropdown-placement-bottomLeft {
        -webkit-animation-name: unset;
        animation-name: unset;
        -webkit-animation-duration: .05s;
        animation-duration: .05s;
    }

    .ant-select-dropdown.slide-up-appear.slide-up-appear-active.ant-select-dropdown-placement-topLeft, .ant-select-dropdown.slide-up-enter.slide-up-enter-active.ant-select-dropdown-placement-topLeft {
        -webkit-animation-name: unset;
        animation-name: unset;
        -webkit-animation-duration: .05s;
        animation-duration: .05s;
    }

    .ant-select-dropdown.slide-up-leave.slide-up-leave-active.ant-select-dropdown-placement-bottomLeft {
        -webkit-animation-name: unset;
        animation-name: unset;
        -webkit-animation-duration: .05s;
        animation-duration: .05s;
    }

    .ant-select-dropdown.slide-up-leave.slide-up-leave-active.ant-select-dropdown-placement-topLeft {
        -webkit-animation-name: unset;
        animation-name: unset;
        -webkit-animation-duration: .05s;
        animation-duration: .05s;
    }