方法：动态绑定类名

active 是高亮类名。

<div class="tab-bar">
     <span class="item" :class="{ active: tag == '全部' }" @click="tag = '全部'">全部</span>
     <span class="item" :class="{ active: tag == '欧美' }" @click="tag = '欧美'">欧美</span>
     <span class="item" :class="{ active: tag == '华语' }" @click="tag = '华语'">华语</span>
     <span class="item" :class="{ active: tag == '流行' }" @click="tag = '流行'">流行</span>
     <span class="item" :class="{ active: tag == '说唱' }" @click="tag = '说唱'">说唱</span>
     <span class="item" :class="{ active: tag == '摇滚' }" @click="tag = '摇滚'">摇滚</span>
</div>

    data() {
        return {
            //当前选择的标签数据  默认选择全部
            tag: "全部",
        };
    },