.slider {
  position: relative;
  overflow: hidden;
  margin: 0px auto 0 auto;
}

    .slider ul {
        position: relative;
        margin: 0;
        padding: 0;
        list-style: none;
        white-space: nowrap;
        width:200%;
    }

        .slider ul li {
            position: relative;
            display: block;
            float: left;
            margin: 0;
            padding: 0;
            width: 735px;
            height: 350px;
            text-align: center;
        }

    .slider .control_prev, .slider .control_next {
        position: absolute;
        top: 39%;
        z-index: 999;
        /*padding: 4% 3%;*/
        width: 4%;
        max-width: 30px;
        height: 20%;
        min-height: 30px;
        background: rgba(255,255,255,.5);
        color: #fff;
        text-decoration: none;
        font-size: 14px;
        opacity: 0.8;
        cursor: pointer;
        /*display: flex;*/
        display: none;
        flex-direction: column;
        justify-content: center;
        align-items: center;
    }

    .slider:hover .control_prev, .slider:hover .control_next {
        display: flex;
    }

    .slider .control_prev:hover, .slider .control_next:hover {
        opacity: 1;
        -webkit-transition: all 0.2s ease;
    }

    .slider .control_prev {
        border-radius: 0 2px 2px 0;
    }

    .slider .control_next {
        right: 0;
        border-radius: 2px 0 0 2px;
    }