Detailed explanation of how to modify the style of el-select: popper-append-to-body and popper-class

<el-select
    :popper-append-to-body="false"
    v-model="taskType"
    placeholder="Please select"
    size="mini"
    class="select-style"
    popper-class="select-popper"
  >
    <el-option
      v-for="(item,index) in taskTypes"
      :key="index"
      :value="item.value"
      :label="item.label"
    ></el-option>
  </el-select>

.select-style {
    width: 3rem;
    margin-right: 0.36rem;
    /deep/.el-input__inner {
      border-top-left-radius: 0;
      border-bottom-left-radius: 0;
      border: 1px solid #a1a3ad;
      border-left-width: 0;
      background-color: rgba(0, 0, 0, 0.8);
      font-family: PingFangSC-Regular;
      font-size: 0.28rem;
      color: rgba(255, 255, 255, 0.6);
    }
  }

/deep/.select-popper {
    background-color: $item-bg-color;
    border-radius: 0.08rem;
    border: solid 0.02rem #1c395d;
    font-family: PingFangSC-Regular;
    .el-select-dropdown__item.selected {
      font-family: PingFangSC-Regular;
      font-size: 0.28rem;
      color: rgba(74, 141, 253, 1);
    }
    li {
      color: #fff;
      background: transparent;
      color: #fff;
      font-size: 0.28rem;
    }
    .el-select-dropdown__item:hover,
    .el-select-dropdown__item.hover {
      background-color: rgba(110, 147, 206, 0.2);
      margin-right: 1px;
    }
    .popper__arrow::after {
      border-bottom-color: $item-bg-color;
    }
    .popper__arrow {
      border-bottom-color: $item-bg-color;
    }
    .el-select-dropdown__empty {
      padding: 0.2rem;
      font-size: 0.28rem;
    }
  }