给div设置一个v-show，当点击叉号按钮时，将v-show控制div显示的属性设置为false即可

<div class="dia" v-show="showDiaBox">
    <div class="bigtitle">
        <span class="lefttitle">模型基础属性</span>
	        <span class="closeicon" @click="closeDiaBox">
	        <i class="el-icon-circle-close" style="font-size: 24px"></i>
        </span>
    </div>
</div>

export default {
	data(){
		return{
			showDiaBox: true
		}
	},
	methods: {
        closeDiaBox() {
            this.showDiaBox = false
        }
    }
}