NEZ-2480 fix：下拉框无内容样式问题

nezha-fronted/src/components/page/alert/alertMessage.vue

@@ -35,7 +35,7 @@
         >
           <template v-slot:before>
             <div>
-              <el-dropdown-item :disabled="batchDeleteObjs.length==0">
+              <el-dropdown-item :disabled="batchDeleteObjs.length==0" :class="'nz-el-dropdown-menu-item'">
                 <delete-button
                   ref="deleteButton"
                   :single="false"
@@ -53,7 +53,7 @@
                   :type="'link'"
                 ></delete-button>
               </el-dropdown-item>
-              <el-dropdown-item :disabled="batchDeleteObjs.length==0">
+              <el-dropdown-item :disabled="batchDeleteObjs.length==0" :class="'nz-el-dropdown-menu-item'">
                 <div id="alert-msg-batch-ack" v-has="'alertMessage_expired'" @click="batchAck"><i class="nz-icon nz-icon-queren"></i>{{$t('overall.batchAck')}}</div>
               </el-dropdown-item>
             </div>