效果如图：

1.popper-append-to-body设置为false  同级添加class名

 <el-select v-model="handleTemp.game_id" placeholder="请选择" class="select_style" :popper-append-to-body="false">
      <div slot="empty" class="select_input">
          <el-button
            size="mini"
            type="text"
            icon="el-icon-finished"
            class="buttonSty"
            @click="selectAll('game_id')"
            >全选</el-button
          >
          <el-button
            size="mini"
            type="text"
            icon="el-icon-close"
            class="buttonSty13"
            @click="clearSelectAll('game_id')"
            >清空</el-button
          >
          <el-button
            size="mini"
            type="text"
            icon="el-icon-sort"
            class="buttonSty13"
            @click="reverCheck('game_id')"
            >反选</el-button
          >
          <div class="ml-10 mr-10 mb-5">
            <el-input
              ref="searchDom3"
              v-model="dropDownValueGame"
              @input="dropDownSearch('game_id')"
              style="width: 100%"
              size="mini"
              placeholder="请搜索"
            >
              <i slot="prefix" class="el-input__icon el-icon-search"></i>
            </el-input>
            <div
              style="font-size: 12px; color: #606266"
              class="pl-10 pr-20 mt-10 mb-10"
            >
              暂无匹配数据...
            </div>
          </div>
        </div>
</el-select>

 属性说明：

样式参考

<style scoped lang="scss">
.select_style {
  ::v-deep {
    .el-select-dropdown__list {
      padding: 0;
    }
    .select_input {
      position: sticky;
      top: 0;
      left: 0;
      width: 100%;
      z-index: 9999;
      background-color: #fff;
    }
  }
}
</style>