SOURCE

<div id="app">
    <!-- :class="{ "class名称" : true / false }" -->
    <div class="radio" :class="{ 'radio-selected' : radioSelected }"></div>

    <hr />
    <button @click="changeRadio()">{{radioSelected?'反选':'选中'}}</button>
</div>



<script>
    var app = new Vue({
        el:'#app',
        data:{
            // 是否添加 radio-selected 样式
            radioSelected:false
        },
        methods:{
            // 改变 radioSelected 的值
            changeRadio:function() {
                this.radioSelected = !this.radioSelected;
            }
        }
    })
</script>

.radio {
    width: 32px;
    height: 32px;
    border-radius: 50%;
    border: 1px solid #777;
}

/* 用于动态添加的类 */
.radio-selected {
    background: red;
}