动态设置class名称

        <div class="first_tab_item pointer" :class="{first_tab_item_active: tabIndex<4}" @click="changeTab(0)">
              <i class="iconfont icon-yiliao"></i>{{ $t('product.tabText1') }}
        </div>

      .first_tab_item_active {
        color: #fff;
        background: linear-gradient(-26deg, #74C7FC, #699BF9);
      }