nav动态修改背景颜色

	mounted(){
		this.clientHeight=this.$refs.bgDiv.clientHeight-this.$refs.nav.$refs.navBar.clientHeight
		const scroll=() =>{
			var scrollTop =
        document.documentElement.scrollTop || document.body.scrollTop
			if(scrollTop>this.clientHeight){
				this.bg='#696BF5'
				this.title='星级节点会员线上投票'
			}else{
				this.bg='transparent'
				this.title=''
			}
		}
		this.scroll=scroll
		window.addEventListener('scroll',scroll)
	},
	destroyed(){
		window.removeEventListener('scroll',scroll)
	},