l-echart层级高于自定义底部导航，怎么解决

   <cover-view class="cu-bar tabbar bg-white shadow foot" style="background-color: #ffffff">  
        <template v-for="(tabbar,index) in tabbarList" :key="index">  
            <cover-view class="action" @click="changeTabbar(index)" :data-cur="index"  
                style="position: relative;z-index: 999;">  

                    <cover-view class="icon cloudfont " :class="tabbar.icon"  
                        style="position: relative;z-index: 999; font-size: 50rpx;" :style="['color:'+tabbar.color]">  
                    </cover-view>  
                    <cover-view :style="['color:'+tabbar.color]">{{tabbar.name}}</cover-view>  

            </cover-view>  
        </template>  
    </cover-view>