<div class="flex">
　　<label>城市</label>
　　<div class="dealerbo">
　　<select><option value="110000">北京市</option></select>
　　</div>
</div>

.flex {

 width: 30%;

 color: #2D3E4E;

 font-size: 15px;

 border-bottom: 1px solid rgba(45, 62, 78, 0.3);

 margin-right: 5%;

}

label {

 text-align: left;

 width: 100%;

 display: inline-block;

 margin-bottom: 5%;

 font-weight: 600;

 font-size: 15px;

}

.dealerbo {

    border-bottom: 1px solid rgba(255, 255, 255, 0.5);

    position: relative;

    width: 99%;

    align-items: center;

    justify-content: space-between;

    background: url(../images/arrow_Down.png) no-repeat 100% center;

    overflow: hidden;

    padding-right: 5%;

    white-space: nowrap;

}

select {

    height: 27px;

    font-size: 14px;

    color: #000;

    border: none;

    background-color: transparent;

    padding-bottom: 5px;

    overflow: hidden;

    white-space: nowrap;

    width: 100%;

    text-overflow: ellipsis;

}

<div class="city">

    <div>

        <select>

           <option value="110000">北京市</option>

       </select>

   </div>

   <div>

        <select>

           <option value="110000">北京市</option>

       </select>

    </div>

</div>

.flex {

     position: relative;

     display: flex;

     flex-wrap: wrap;

     width: 100%;

     margin-bottom: 0.1rem;

     border-bottom: 1px solid rgba(45, 62, 78, 0.3);

}

.flex label {

 text-align: left;

 width: 100%;

 display: inline-block;

 margin-bottom: 2%;

 font-weight: 600;

}

.city {

    position: relative;

    display: flex;

    border-bottom: 1px solid rgba(255, 255, 255, 0.5);

    width: 100%;

}

.city::before {

    content: '';

    border-right: 1px solid #ddd;

    height: 20px;

    width: 1px;

    position: absolute;

    left: 47%;

    bottom: 9%;

}

.city > div {

    position: relative;

    width: 40%;

    display: flex;

    align-items: center;

    justify-content: space-between;

    margin-right: 10%;

}

.popBox .pb .form .flex .city > div::after {

 content: '';

 height: 0.11rem;

 width: 0.22rem;

 position: absolute;

 background: url(../../pc/images/arrow_Down.png) no-repeat 100% center;

 right: 0;

 background-size: 100%;

 bottom: 0.2rem;

}

select {

    height: 27px;

    font-size: 0.28rem;

    color: #000;

    border: none;

    background-color: transparent;

    padding-bottom: 5px;

    overflow: hidden;

    white-space: nowrap;

    width: 100%;

    text-overflow: ellipsis;

}

a, button, input, optgroup, select, textarea {

    -webkit-tap-highlight-color: rgba(0, 0, 0, 0);

}

button, optgroup, select, textarea {

    -webkit-appearance: none;

    outline: none;

    border-radius: 0;

}

select option {

    color: #000;

    font-size: 0.28rem;

}