下滑改变颜色

methods：{

scrollbar(){

if(this.$refs.section.scrollTop>50){

this.$refs.header.style.background="linear-gradient(rgba(255,0,0,0.7),rgba(0,0,0,0))"

}else{

this.$refs.header.style.background="rgba(0,0,0,0)"

}

}

}